Michael T. Griffith


@All Rights Reserved

Fourth Edition

Warren Commission (WC) apologists, along with some conspiracy theorists, have attacked the relevancy of the Dallas police dictabelt recording, which was allegedly made from a patrolman's microphone in Dealey Plaza at the time of the shooting (e.g., Posner 238-242). Prestigious acoustical experts retained by the House Select Committee on Assassinations (HSCA) concluded the tape had on it at least four sound impulses that were caused by gunshots, and that one of the shots came from in front of the presidential limousine (Marrs 530-537). These scientists were Dr. David Barger, Dr. Mark Weiss, and Dr. Ernest Aschkenasy. These men were recommended to the Committee for their expertise by the Acoustical Society of America. Richard Trask explains how the tape initially came to the attention of the Select Committee, and then describes the analyses that were performed on it:

Just weeks before its demise . . . the Committee was given new and startling information. Some time earlier critic Gary Mack, among others, had drawn the attention of Committee staff to the possibility that the noise of gunfire might have been inadvertently recorded on Dallas Police Department dispatch transmissions made on November 22, 1963. The original recordings of these transmissions, made over two separate police radio networks, were located in the possession of a Dallas official. Police transmissions had been recorded on Department Channel 1 by means of a Dictaphone belt recorder and the day of the assassination this channel was used primarily for normal police activities. Channel 2 was used that same day as a communications link for the presidential motorcade. It was voice-activated and recorded on a Gray Audiograph Disk at headquarters. Though Channel 2 was apparently not in use during the period when the actual assassination occurred, by a fluke of a microphone transmitter on a motorcycle or other vehicle being stuck on the "On" position, approximately 5.5 minutes of the noises in and around the vehicle were recorded by the Dictaphone belt, including around the time of the shooting.

Though unclear to the unaided ear what among the various noises recorded on the Dictabelt meant, several critics postulated that among the clatter were a number of possible gunshots. The Committee decided to give this problem over to acoustics experts. These respected acoustics scientists would analyze the nature and origin of the suspect sound impulses on Channel 1 to determine if sounds of shots had been recorded; and if so, how many, the time interval, and point of origin. In May 1978 the Committee contracted with Bolt, Beranek and Newman, Inc. [BBN], to attempt the analysis. By means of sophisticated and, to the layman, complicated scientific analysis of the recordings, chief scientist Dr. James Barger located 6 impulse sequences which could have been caused by a loud noise such as a gunshot. The Committee was urged to conduct an acoustical reconstruction of the assassination at the Dallas site. Realizing that Barger's initial findings, if true, pointed to a probable assassination conspiracy, the Committee sought an independent review of his analysis by Queen's College, New York, professor Mark Weiss and his research associate, Ernest Aschkenasy. Barger's analysis and methodology for the reconstruction were concurred by the two others, and on August 20, 1978, an elaborate test in Dealey Plaza was conducted. Microphones were strategically located at 36 separate positions to record test shots fired from the sixth floor southeast corner of the Texas School Book Depository Building window and from the area behind the stockade fence on the grassy knoll from where various witnesses believed shots to have been fired. A total of 432 shot impulse sequences were recorded. These "acoustical fingerprints" were then laboriously compared with the six impulses noted on the original recording for a total of 2592 comparisons. This analysis was not completed until days before Barger's public hearing on September 11. Though cautioning that the match he had found did not prove conclusively that the impulses on the 1963 recording represented gunfire, Barger testified that his studies showed that the 1963 recording contained four sounds attributed to probable gunshots. Three of the impulses matched an origin point at the Texas School Book Depository sixth floor, and one impulse, the third in the sequence, matched an origination point on the grassy knoll. He further cautioned his findings of the grassy knoll sound to a probability of 50 percent.

Asked by the Committee to further study Barger's work to obtain more certain results of his possible grassy knoll shot, Weiss and Aschkenasy put together an analytical extension to refine the estimate. They studied Dealey Plaza determining which structures were likely to have caused echoes received by the microphones. By identifying these echo-generating sources around the vicinity of the knoll, there were able to predict what "sound fingerprints" would have been created by a shot from the grassy knoll location when picked up by an open microphone. Each location of a microphone relative to a shooter's location would, by echoes generated off constant structures, produce a unique sound travel pattern which they referred to as a "sound fingerprint." The experts were confident that their precise calculations, taking numerous variables including air temperature in 1963 and buildings structured after 1963 into consideration, gave them a certainty factor of 95 percent or better, that impulse number 3, previously identified by Barger, was in fact a shot fired from the grassy knoll. (Trask 131-132)

David Scheim, who holds a doctorate in mathematics from the Massachusetts Institute of Technology, discusses the dictabelt and its validity as proof of multiple gunmen:

Indeed, there were important additional elements that corroborated the conclusion of Barger, Weiss and Aschkenasy. The positions they determined for the motorcycle at the time of the four shots traced out a path on Houston Street that fit the actual course and speed of the motorcade. . . . Moreover, an "N-wave," characteristic of supersonic gunfire, appeared in each dictabelt impulse for which the police microphone was in an appropriate position to detect it, including the recorded sound of the third shot [identified by the Committee as coming from the grassy knoll]. The most striking find, however, was the exact location of the grassy knoll gunman. According to the acoustical calculations, this firing position was behind the picket fence, eight feet west of the corner. That was just TWO TO SEVEN FEET from where S. M. Holland, a dozen years earlier, had placed the signs observed by himself and fellow railroad workers: the puff of smoke, muddy station wagon bumper, cigarette butts, and a cluster of footprints. (25:36, original emphasis)

Robert Blakey, the former chief counsel for the HSCA, describes some of the testimony that Drs. Weiss and Aschkenasy gave to the Committee regarding the grassy knoll shot:

In clear and forceful terms, Weiss and Aschkenasy reviewed their work. They had become involved at first only to review Barger's proposed test in Dallas in August. After Barger's September testimony, they had been asked to try to move the uncertainty off center "either way." They started their work in October and finished in late December. The result was "a probability of 95 percent or better [that] there was indeed a shot fired from the grassy knoll." They were, they said, able to place the shooter within a five-foot "circumference." They could pinpoint the location of the microphone to within a foot and a half. They knew that the weapon had fired a super-sonic bullet, since a shock wave had preceded the sound of the muzzle blast (they could detect both phenomena on the tape). The weapon could have been a rifle or a pistol, since either could fire super-sonic ammunition. They explained how they knew the [policeman's] microphone had been shielded at various points by the windshield of the motorcycle.

In their calculations, they had made allowances for a possible small error on the scale map they had used (less than one foot); air-temperature and humidity variances; and the characteristics of the type of radio equipment used by the Dallas police in 1963. They had double-checked their calculations, and, yes, they were satisfied with their conclusions "beyond a reasonable doubt." In addition, the scientific principles they had employed were little more than "high school physics and geometry." Anyone who had heard an echo could understand what was involved.

No, the sound [of the grassy knoll shot] could not have been a motorcycle backfire since it was preceded by the supersonic shock wave. In any event, there was no motorcycle behind the picket fence. Obviously, the bell tolling on the tape had come from somewhere other than Dealey Plaza. Could the sound of the grassy knoll shot also have come from a different area? Only if the other area were an exact acoustical replica of Dealey Plaza, and shots had been fired there too. "If somebody were to tell me that the motorcycle was not in Dealey Plaza," Aschkenasy noted, "[that] he was transmitting from some other location. . . . I would ask to be told where that location is, . . . I would go there, and, . . . I would expect to find a replica of Dealey Plaza. . . ." The shot had not been fired up in the air, they said, but at the presidential limousine. No, the sound of the grassy knoll shot could not have been an acoustical mirage. The distance was too short, and the sequence of echoes was inconsistent with a mirage. The conclusion was, they said, inescapable; it was not a matter of interpretation; there "didn't seem to be any way to make those numbers go away, no matter how hard . . . [they] tried." (Blakey and Billings 116-117)

The tape is an important piece of evidence because it clearly seems to scientifically prove that more than three shots were fired, and that at least one of the shots came from the front. If the findings of the HSCA's acoustical experts are correct, then the tape does indeed contain sounds caused by four shots, and one of those shots was fired from the grassy knoll (which was in front and to the right of the president's limousine during the shooting).

I would like to emphasize, however, that the HSCA's claims about the tape have not been absolutely scientifically confirmed to the satisfaction of all researchers. There are questions about the Select Committee's conclusions. For example, the absence of any crowd noises on the tape's first channel would seem to prove the motorcycle was not in Dealey Plaza, since crowd noises can be heard on the second channel. Also, a crucial "cross-talk" transmission by Sheriff Bill Decker on the tape's second channel appears to show that the sound impulses identified as shots don't occur until after 12:31, i.e., at least a minute after the gunfire would have been heard in Dealey Plaza. The explanations offered by defenders of the HSCA's acoustical study to explain these difficulties seem credible and persuasive, but some scientists continue to questions the acoustical evidence.

On the basis of these and other problems, some researchers reject the work of the HSCA's acoustical experts and instead accept the findings of a special panel of the National Academy of Sciences (NAS). But there are problems with relying on the Academy's work. Not only did the NAS panel members fail to examine items of evidence that supported the HSCA's findings, but they conducted their work in secret and would not make their raw materials available so other experts could try to duplicate their work. In addition, the NAS scholars utilized a faulty transcript of the dictabelt recording, and, according to W. Anthony Marsh and others, found it necessary to manipulate the times of the transmissions on the tape, in one case by almost a minute, in order to reject the HSCA's conclusions (Marsh). On the other hand, critics of the acoustical evidence claim that the NAS study is superior to that of the Select Committee's, and that the NAS panel members were just as qualified as the HSCA's scientists, if not more so. It should be pointed out, however, that the NAS panel members were not acoustical experts.

The chairman of the NAS panel, Dr. Norman Ramsey, reported that he found a number of flaws in the work of the HSCA's acoustical experts. Said Dr. Ramsey,

The impulses selected for the BRSW study [i.e., part of the HSCA study] were not always the largest impulses. Frequently, large impulses were omitted and some impulses close to the noise level were retained. There are far more impulses that do not fall into the BRSW classification of "probably sounds of gunfire" than do. Since the results of the correlation coefficient calculations are highly dependent on the impulse and echo pattern selection process, it is especially critical that the scheme used to distinguish these sounds stand up to close scrutiny, with the process being spelled out in detail so others can duplicate the analysis. From the published reports, IT IS IMPOSSIBLE TO DO SO. Furthermore, weak spikes on the Dictabelt often are selected to correspond to strong patterns, in the test patterns and vice versa. (Livingstone 363, original emphasis)

Scheim has commented on the work of the NAS panel as follows:

While the panel offered some valid criticisms of the methodology used in the House acoustical studies, it introduced complex and controversial assumptions and made several errors of its own. In a letter of February 18, 1983, Dr. Barger noted enigmatic features in a recording upon which the National Academy of Sciences panel relied and pointed out that it "did not examine the several items of evidence that corroborated our original findings." Barger stood by the acoustical determination of a grassy knoll shot as accepted by the House Select Committee on Assassinations. (Scheim 35-36)

Scheim continued,

. . . the critical Weiss-Aschkenasy conclusion of a 95-percent probability of a grassy knoll shot was treated only in a sketchy three-page appendix [in the NAS panel's report] that made one outright error--there was only one degree, not two, of freedom associated with the position of the shooter along the grassy knoll fence. This appendix also recalculated the probability by subtracting degrees of freedom adjusted in the Weiss-Aschkenasy analysis from matches obtained, an arbitrary approximation to a complex mathematical calculation, akin to computing the volume of a cube as three by adding its dimensions. The appendix itself included the admission that this critical calculation was "possibly overconservative" and "may be unduly conservative." (Scheim 431 n 120)

Gary Cornwell, the former deputy chief counsel for the HSCA, likewise takes issue with the NAS study. Note: Cornwell refers to the NAS panel and report as the NRC panel and report, since the panel was actually assembled by the National Research Council (NRC), whose members are drawn from the NAS. Says Cornwell,

The findings of Bolt, Beranek and Newman--like almost everything in the Kennedy case--have subsequently been questioned by the FBI, and by a panel assembled by the National Research Council (whose members are drawn from the Councils of the National Academy of Sciences. . . .). According to a "Notice" on the first page of the NRC report, the committee that studied the BBN findings "was chosen for their special competence and with regard for appropriate balance"--not because they were acoustics experts, which they were not.

I personally found it interesting not only that the NRC found that it had conclusively disproved the Select Committee's acoustical report and that there was no need for further study, but also that—remarkably, and just as with the findings of the Warren Commission--there was not a single dissent among any of the panel's members. (It may or may not also be relevant that, among the most vocal of the panel's members was a scientist who, before joining the panel and reviewing the acoustical study in detail, had taken strong positions in support of the Warren Commission's findings. . . .)

The NRC's principal rationale for rejecting the findings of Bolt, Beranek and Mark Weiss was that the Channel I tape contained "cross-talk" from Channel II that indicated that the portion of the Channel I tape containing the four impulse patterns identified as gunfire occurred at least 30 seconds after the actual assassination. The NRC offered possible (plausible) explanations as to various ways that such cross-talk could have gotten onto Channel I, including that the stuck microphone on Channel I was positioned near another microphone that was monitoring Channel II, and that the words being transmitted over Channel II were picked up (very faintly) by the stuck Channel I microphone, and transmitted and recorded on the Channel I Dictabelt in the police station. Subsequent re-recording is another possible explanation. The NRC in the end was not able to definitely state the cause. Nor were they able to verify that the Channel I tape they analyzed was the original DPD tape, and thus could not say for sure that the cross-talk had been recorded on November 22, 1963. Finally, subsequent private analysis as well as further review by Dr. Barger has revealed that the NRC's tests appear to have been conducted with the tapes being run at an improper speed, thus invalidating their calculations of when the impulse patterns at issue actually did occur in relation to the assassination.

And the NRC essentially ignored, and never did explain how, if these impulse patterns were not gunfire, their timing, sequencing, and qualitative characteristics were so extensively corroborated by the other physical and scientific evidence in the case. Was all of the meshing of such evidence simply a coincidence? . . . Several witnesses testified that one shot came from the grassy knoll, just as the acoustics indicated. Just a coincidence? The shock waves and windshield distortions were present on the shots where they should have been, and absent on the others. One more coincidence? Since the NRC described their findings as conclusive and not subject to question, one must wonder why the NRC ignored all of this evidence that corroborated the Barger and Weiss findings, but is totally inconsistent with the NRC findings that these impulses are not the actual sounds of gunfire. One might also wonder why the NRC never addressed, never discussed, and never attempted to explain other "cross talk" on the Channel I tape that is totally inconsistent with the NCR conclusion that impulse patterns evidencing four shots occurred 30 seconds after the actual assassination. (Cornwell 112-114)

The HSCA identified the microphone of police officer H. B. McClain as the mike that recorded the sounds on the tape, but McClain later insisted that his cycle was in the wrong location to have done this, and according to some researchers, including some conspiracy theorists, the photographic evidence proves that McClain was correct (e.g., Livingstone 358). Posner sees McClain's denial as evidence against the dictabelt recording. The NAS panel likewise appealed to McClain's denial. McClain said he couldn't have recorded the sounds on the tape because he accompanied the President's limousine to Parkland Hospital and had his siren on en route to the hospital. "Yet," says Posner, "on the dictabelt recording there are no sirens" (Posner 240). However, some researchers have countered by claiming that a UPI photograph shows McClain was still in Dealey Plaza after the limousine had departed for the hospital (Marrs 533; Scheim 35). But critics of the tape reply that the Hughes film shows that McClain "was barely past the intersection of Houston and Main streets when the shooting began" and that therefore he was not in a position to record the shots anyway (Livingstone 358; Scally 38). In addition, former Committee chief counsel Blakey has indicated that McClain left for the hospital at right about the same time the limousine departed (Blakey and Billings 117). One of the HSCA's acoustical experts stated that the sound of sirens would not have been audible over the noise of the motorcycle's engine anyway (Scheim 35).

Critics of the acoustical evidence argue that a strong case can be made that McClain's mike was not the one that recorded the sounds on the tape. I should add, though, that according to defenders of the HSCA's findings, the acoustical evidence is not dependent on the assumption that the open microphone was Officer McClain's. Christopher Scally argues that Officer Bobby Hargis's mike could have recorded the sounds on the dictabelt tape (Scally 37-43). Says Scally,

In his testimony before the HSCA on December 29, 1978, Dr. Barger said that, having slowed down, the level of engine noise remained constant for 30 to 40 seconds. It then rose to an even higher pitch than it had earlier reached, and then remained at this high level for at least two minutes. In a letter to Bob Cutler dated February 2, 1979, Dr. Barger disclosed that the motorcycle engine was, in fact, IDLING after the shots were fired, before apparently moving off at high speed.

A detailed study of the photographic evidence showed that the actions of police motorcyclist Bobby W. Hargis were entirely consistent with these facts. Hargis, who was riding approximately 10 feet behind and immediately to the left of the President, can be seen in many photographs taken in Dealey Plaza. His testimony before the Warren Commission can be verified by reference to these photographs. . . .

Film of the motorcade on Elm Street shows that Hargis stopped his motorcycle immediately after the final shot. Bond 4 and Bothun 4, two still photographs taken 20 and 26 seconds later respectively, show Hargis returning to his motorcycle and remounting it, exactly as he testified. . . .

Unlike those of McClain, the actions of Officer Hargis correspond exactly with those which must have occurred in order to generate the motorcycle engine noises found on the radio recording. . . .

Researcher Stephen Barber has recently analyzed these sounds in great detail. His study confirms the sound of the idling engine, and also the sound of another motorcycle passing the one which is stationary. This second motorcycle is, in fact, the one ridden by Officer McClain, who can be seen riding past Hargis' stationary motorcycle in the Bond photograph taken 20 seconds after the final shot. Just after McClain goes by, Barber detects the sound of Hargis snapping his kick-stand into place as he prepares to leave the scene. During the next 15 seconds Barber notes the echo of Hargis' engine as he passes through the Triple Underpass. For the next 20 seconds, according to Barber, the engine noise reverts to an "idling" sound. It may well be, however, that this simply the drop in engine noise level which would follow as Hargis emerges from the tunnel and scans the area, exactly as he testified. [Hargis indicated that he slowed down after going through the triple underpass in order to scan the area to see if anyone was running away from the plaza.] The noise level rises again, however, as Hargis circles round and returns to the TSBD, from where he transmitted on Channel 2 of the police radio between 12:34 and 12:35 pm. It was during the latter part of the return journey that Hargis recorded the sound of sirens approaching and receding, and it is quite possible that these sirens were on vehicles which passed Hargis, going in the opposite direction towards Parkland Hospital.

This reconstruction of Hargis' movements is consistent with Dr. Barger's finding that, following the period of idling immediately after the shots were fired, the motorcycle accelerated and remained in motion for 2 to 3 minutes. It also answers most, if not all, of the outstanding questions about the identity of the motorcycle policeman with the jammed transmitter. (Scally 39-42, original emphasis)

Scally concedes that his scenario does raise one new question: If Hargis was the source of the interference on channel 1 between 12:28 and 12:33, how could the following exchange have taken place on channel 2 less than two minutes later:

HARGIS. A passer-by states the shots came from the Texas School Book Depository Building.

DISPATCHER. Get all the information.

Scally says there are three possible explanations, "any one of which, if true, would be satisfactory" (Scally 42). He continues by presenting these explanations:

- Hargis realized his transmitter was switched to Channel 1, and he simply turned it back to Channel 2. This possibility was not discussed during his testimony before the Warren Commission, nor is it mentioned in the HSCA's published evidence.

- The fault in his radio caused it to alternate between Channels 1 and 2, and it had reverted to Channel 2 automatically by the time he returned to the Book Depository and spoke to the dispatcher.

- His Channel 2 transmission was made over a different radio. This is at least possible, since Hargis undoubtedly parked his motorcycle near the TSBD and then moved around the area on foot. He could therefore easily have used another radio to make his transmission on Channel 2. Once again, however, neither Warren Commission testimony nor the HSCA's final report address this possibility. (Scally 43-44, original emphasis)

But critics of the acoustical evidence argue that the sirens on the tape prove that the motorcycle was not with the motorcade. "There is no possible way," says Todd Wayne Vaughan, "in which this cycle was with the President's motorcade. It's a physical impossibility" (Livingstone 351). Vaughan explains,

Beginning at 262 seconds and lasting until 299 seconds [on the tape] are the sounds of several sirens. These sirens are very important as to determining the location of the cycle with the open mike. The sirens are the sirens mounted on the motorcade vehicles. They were all turned on following the assassination. The sirens on the tape sound as if they are passing a stationary microphone not in the motorcade but on Stemmons Freeway. The sirens rise in intensity, fade, rise again, and fade again. This continues and suggests that several vehicles are passing the open mike. It is clear that the open mike is not in the motorcade but somewhere on Stemmons Freeway. (Livingstone 351)

Harrison Livingstone raises the issue of why no shots are audible on the tape and cites this as another reason that the motorcycle could not have been in Dealey Plaza:

Why, now, are there no shots audible on the tape? Rifle shots in such an enclosed urban space, echoing off buildings, would be very loud and certainly were heard by everyone in Dealey Plaza. Was there some technical reason that they might not record through an open mike located somewhere in Dealey Plaza? The answer is that there was no microphone open anywhere near Dealey Plaza, and so the gunshots could not have been recorded. (Livingstone 357)

It must be remembered that the HSCA's acoustical scientists identified certain sound impulses on the tape as gunshots. One cannot play the dictabelt and hear gunfire. It is not audible.

WC supporter Jim Moore gives some of his reasons for rejecting the dictabelt recording as evidence of multiple gunmen:

Not once in its final report did the HSCA address how a gunman firing from the knoll might have missed, nor did it speculate on where the bullet hit. Having rushed to judgment on the issue of the dictabelt and the recording showed, the Committee dissolved itself with the admonition that it was unable to identify the other gunman and that the Department of Justice should examine the audio evidence to see if it concurred with the Committee's findings.

Of course, the Justice Department did not concur, nor did the National Academy of Sciences. The NAS review, in particular, discovered the existence of "bleedover" on the Dictabelt at the time of the assassination [actually, the bleedover was brought to the NAS panel's attention by a private researcher]. This bleedover [i.e., the Decker transmission] contained dialogue between law enforcement officers that indicated the portion of the recording where shots were found had actually been recorded a minute or so after the assassination. (Moore 142-143)

Defenders of the dictabelt contend that the problems noted in the tape are outweighed by the presence of the N-wave, by the correlations between the tape and the motorcade's movement, and by the fact that the sound for the posited grassy knoll shot was determined to come from the same area from which several witnesses said shots were fired. Defenders of the tape also note that the acoustical fingerprint for the grassy knoll shot matched point for point all of the 26 impulses of the test shot fired from the knoll during the Committee's site simulation. Additionally, some researchers maintain that the tape in evidence is a copy, and there is some evidence that this is the case. This, they claim, could explain the technical discrepancies that have been found in the recording.

What about the gaps in the recording? And what effect could they have on the timing of the transmissions? Defenders of the tape note that faulty time-keeping by the dispatchers, and the fact that there's no way to know how long the machine was turned off during the two recordings, might explain Sheriff Decker's seemingly problematic transmission.

During the broadcasts, the Dallas dispatcher notes the time every so often, but is subject to some error by the angle at which he had to look at his clock, and the FBI and Dallas Police found in a test with stopwatches in 1964 that the time was often out by as much as one minute. There were three different dispatchers working at the time of the assassination, and they used three different clocks. The clocks got out of synchronization by as much as one minute over the course of a month before they were reset. During the assassination, there was a great deal of confusion and pressure, and the time checks could not be expected to be perfectly accurate. And the Channel 2 recording had stopped twice at Curry's two transmissions: his "at the underpass" report and his "Parkland Hospital" transmission. The BBN report states clearly that there is no way of knowing how long the machine was off during the two recordings.

Vaughn and Barber equated the two tape times to each other nevertheless, using the simultaneous transmissions by Decker on Channel 2 and both faint and incomplete on Channel 1, a few seconds after the last shot. The "gap" is not on Channel 1. (Groden and Livingstone 254-255; Note: Livingstone no longer accepts the validity of the HSCA's conclusions about the recording.)

If all of the Committee's conclusions about the dictabelt are accepted as accurate, then one must believe that the grassy knoll shooter somehow missed the entire limousine, even though he was only 111 feet away from it, and that the three other shots all came from the alleged sniper's nest. Few researchers believe the shooting occurred in this manner.

Some defenders of the acoustical evidence assert that the HSCA simply mismatched the impulses on the tape with the Zapruder film. The Committee said the fourth impulse (or "shot") on the tape was the fatal head shot. But some researchers maintain that if the third impulse is aligned with the head shot, then every other impulse matches an action in the Zapruder film. In fact, Robert Groden, who served as a consultant to the Select Committee on certain issues, claims that he met with Weiss and Aschkenasy and that the three of them found that the third impulse was the best match for the head shot. But, according to Groden, the Committee's chief counsel, Blakey, would not allow him to express this position in his testimony. Matthew Smith:

Said Groden, "In all likelihood, the fatal shot did not come from the Book Depository, but rather from the grassy knoll; whether or not Lee Oswald was firing, someone else had actually killed the President." He went on to describe how when the fourth shot was matched up to the pictures of the President's head "exploding," none of the other shots were in alignment with the [Zapruder] film. But when the third shot was advanced to match up with those pictures "every other impulse matched an action on the film exactly." In High Treason, Groden recounted how Professor Blakey took him aside and ordered him not to express to the Committee any conclusions that he had drawn from his study of the film and tapes. The Congressmen (and the world) were to be told that the fatal shot came from the rear, and the fourth shot was the only one to be considered the head shot. (Smith 147, original emphasis)

Leaving aside the issue of which impulses best match the head shot in the Zapruder film, other researchers doubt Groden's claim that he was denied the opportunity to share his alleged finding with the Select Committee. They wonder why Groden didn't say something about it during his testimony anyway, since he was under no legal obligation to remain silent about it. How could Blakey have prevented Groden from mentioning this important finding once he had begun his public testimony? Would Blakey have dared to interrupt Groden, in front of the Committee and the press, with TV cameras rolling, to tell him not to say another word on the subject? Since Blakey could have taken no legal action against Groden for revealing this finding during his testimony, what would Groden have had to fear anyway? And wouldn't Weiss and/or Aschkenasy have later said something about the supposed correlation between the third impulse and the head shot?

Could it be that the dictabelt tape itself was recorded in Dealey Plaza during the shooting, and that there are indeed four (or more) gunshot impulses on it, but that the Committee's conclusions about the geographical origin of the shots are in error? It must be remembered that the Committee limited the test firings to the sixth-floor window and to one spot on the grassy knoll. No test shots were fired from any of the other locations that had long been suggested by researchers as possible firing positions, such as the Dal-Tex Building, the roof of the TSBD, and the area of the triple underpass. This was a serious mistake. Scally explains:

The HSCA's decision to conduct test firings from the Book Depository and the knoll alone had serious repercussions, because in ignoring other possible firing points, they ruled out the likelihood that any of the unmatched sounds on the police radio tape could be impulses caused by shots from other locations such as, for example, the Dal-Tex building. (Scally 35)

Moreover, Scally maintains that the Committee's acoustical experts were unable to match the second alleged shot on the tape with any of the test shots from the Depository Building:

. . . examination of the correlations between the test shots and the sounds on the Dallas police tape shows that all of the matches with shots at this target were ultimately rejected as "false alarms." It seems there is no acoustical or other evidence to prove that the second shot was fired from the Book Depository! (Scally 35, original emphasis)

In summary, there is good evidence that supports the Committee's acoustical findings. Further study of the dictabelt tape could be done to make it indisputable that it contains the sounds of four or more gunshots. Among other things, a new, more thorough site test should be conducted. Then, an acoustical fingerprint should be done for every sound on the tape that could be a gunshot. (An acoustical fingerprint was done for the grassy knoll shot, but not for any of the other alleged shots on the tape.)  However, even without additional site tests, the available evidence strongly indicates that the dictabelt tape contains four gunshot impulses.


A study by Dr. D. B. Thomas concludes the HSCA's acoustical findings are valid and that further analysis shows an even higher probability that the dictabelt recording contains the impulse of a shot that was fired from the grassy knoll. Thomas's study was published in the British forensic journal Science and Justice. Thomas's article can be found at the following link: (requires Adobe Acrobat Reader). See Appendix A at the end of this article for a summary of Thomas's article.

Also, in an article titled “Crosstalk: Synchronization of Putative Gunshots with Events in Dealey Plaza,” Dr. Thomas presents evidence that McClain's mike was the mike that recorded the sound impulses. In addition, Dr. Thomas answers various attacks on the acoustical evidence, including the rebuttal done by an FBI forensics expert.

Finally, in a recent book titled Head Shot: The Science Behind the JFK Assassination (Amherst, New York: Promotheus Books, 2010), Dr. G. Paul Chambers responds to the criticisms on the acoustical evidence and makes a strong case that the dictabelt recording contains four gunshot impulses.



Blakey, G. Robert and Richard Billings, Fatal Hour: The Assassination Of President Kennedy By Organized Crime, Berkley Books Edition, New York: Berkley Books, 1992.

Cornwell, Gary, Real Answers: The John F. Kennedy Assassination, Spicewood, Texas: Paleface Press, 1998.

Groden, Robert and Harrison Edward Livingstone, High Treason: The Assassination Of President Kennedy And The New Evidence Of Conspiracy, Berkley Edition, New York: Berkley Books, 1990.

Livingstone, Harrison Edward, Killing The Truth: Deceit And Deception In The JFK Case, New York: Carroll & Graf Publishers, 1993.

Marrs, Jim, Crossfire: The Plot That Killed Kennedy, New York: Carroll & Graf Publishers, 1989.

Marsh, W. Anthony, "The Ramsey Report," Dateline: Dallas, volume 1, numbers 2 and 3, Summer/Fall 1992, pp. 14-16.

Moore, Jim, Conspiracy Of One, Ft. Worth: The Summit Group, 1991.

Posner, Gerald, Case Closed: Lee Harvey Oswald And The Assassination Of JFK, New York: Random House, 1993.

Scally, Christopher, "So Near . . . And Yet So Far": The House Select Committee On Assassinations' Investigation Into The Murder Of President John F. Kennedy, Dallas, Texas: JFK Assassination Information Center, April, 1980.

Scheim, David S., The Mafia Killed President Kennedy, London, England: Virgin Publishing Ltd, 1992. First published under the title Contract On America: The Mafia Murder Of President John F. Kennedy, New York: Shapolsky Publishers, 1988. The retitled 1992 edition is a revised and updated version of the 1988 original.

Smith, Matthew, JFK: The Second Plot, London: Mainstream Publishing, 1992.

Trask, Richard, Pictures Of The Pain: Photography And The Assassination Of President Kennedy, Danvers, Massachusetts: Yeoman Press, 1994. 


"Study Backs Theory Of 'Grassy Knoll': New research puts chance of second JFK gunman at 96%"

By George Lardner Jr.


March 26 - The House Assassinations Committee may have been right after all: There was a shot from the grassy knoll.

THAT WAS THE KEY finding of the congressional investigation that concluded 22 years ago that President John F. Kennedy's murder in Dallas in 1963 was "probably ... the result of a conspiracy." A shot from the grassy knoll meant that two gunmen must have fired at the president within a split-second sequence. Lee Harvey Oswald, accused of firing three shots at Kennedy from a perch at the Texas School Book Depository, could not have been in two places at once.

A special panel of the National Academy of Sciences subsequently disputed the evidence of a fourth shot, contained on a police dictabelt of the sounds in Dealey Plaza that day. The panel insisted it was simply random noise, perhaps static, recorded about a minute after the shooting while Kennedy's motorcade was en route to Parkland Hospital.

A new, peer-reviewed article in SCIENCE AND JUSTICE, a quarterly publication of Britain's Forensic Science Society, says the NAS panel's study was seriously flawed. It says the panel failed to take into account the words of a Dallas patrolman that show the gunshot-like noises occurred "at the exact instant that John F. Kennedy was assassinated."

In fact, the author of the article, D.B. Thomas, a government scientist and JFK assassination researcher, said it was more than 96 percent certain that there was a shot from the grassy knoll to the right of the president's limousine, in addition to the three shots from a book depository window above and behind the president's limousine.


G. Robert Blakey, former chief counsel to the House Assassinations Committee, said the NAS panel's study always bothered him because it dismissed all four putative shots as random noise - even though the three soundbursts from the book depository matched up precisely with film of the assassination and other evidence such as the echo patterns in Dealey Plaza and the speed of Kennedy's motorcade.

"This is an honest, careful scientific examination of everything we did, with all the appropriate statistical checks," Blakey said of Thomas's work. "It shows that we made mistakes, too, but minor mistakes. The main thing is when push comes to shove, he increased the degree of confidence that the shot from the grassy knoll was real, not static. We thought there was a 95 percent chance it was a shot. He puts it at 96.3 percent. Either way, that's 'beyond a reasonable doubt.' "

The sounds of assassination were recorded at Dallas police headquarters when a motorcycle patrolman inadvertently left his microphone switch in the "on" position, deluging his transmitting channel with what seemed to be motorcycle noise. Using sophisticated techniques, a team of scientists enlisted by the House committee filtered out the noise and came up with "audible events" within a 10-second time frame that it believed might be gunfire.

The Warren Commission had concluded in 1964 that only three shots, all from behind, all from Oswald's rifle, were fired in Dealey Plaza as the motorcade passed through. But the House experts, after extensive tests, found 10 echo patterns that matched sounds emanating from the grassy knoll, traveling carefully measured distances to nearby buildings and then bouncing off them to hit the open motorcycle transmitter.

They also placed the unknown gunman behind a picket fence at the top of the grassy knoll, in front of and to the right of the presidential limousine. The House committee concluded that this shot missed, and that Kennedy was killed by a final bullet from Oswald's rifle. Thomas, by contrast, believes it was the shot from the knoll, seven-tenths of a second earlier, that killed the president.


The NAS panel, assigned to conduct further studies after the committee closed down, said in 1982 that the noises on the tape previously identified as gunshots "were recorded about one minute after the president was shot."

The NAS experts, headed by physicist Norman F. Ramsey of Harvard, reached that conclusion after studying the sounds on the two radio channels Dallas police were using that day. Routine transmissions were made on Channel One and recorded on a dictabelt at police headquarters. An auxiliary frequency, Channel Two, was dedicated to the president's motorcade and used primarily by Dallas Police Chief Jesse Curry; its transmissions were recorded on a separate Gray Audograph disc machine.

The shooting took place within an 18-second interval that began with Curry in the lead car announcing on Channel Two that the motorcade was approaching a triple underpass and ended with the chief stating urgently: "Go to the hospital." What seemed to be the gunshots were picked up on Channel One during that interval.

The NAS panel pointed out that Dallas County Sheriff Bill Decker could be heard on both channels saying, "... Hold everything secure ..." seemingly about a half-second after the last gunshot on Channel One. Curry had already told everyone on Channel Two a minute earlier to go to the hospital. As a result, the Ramsey panel concluded that the supposed gunshot noises came "too late to be attributed to assassination shots."

What actually happened was that Curry issued his "go to the hospital" order right after the first shots were fired, wounding Kennedy and Texas Gov. John Connally. The final bullet was fired in almost the same instant that Curry uttered his command. A minute later, Decker, riding in the same car with Curry, grabbed the mike and issued his orders to "hold everything secure."


The study's author said the chances that the National Academy of Science's single-gunman theory was correct were 1 in 100,000.

The NAS experts made several errors, Thomas said, but their biggest mistake was in using Decker's words to line up the two channels. They ignored a much clearer instance of cross talk when Dallas police Sgt. S. Q. Bellah can be heard on both channels, asking: "You want me to hold this traffic on Stemmons until we find out something, or let it go?"

Those remarks come 179 seconds after the last gunshot on Channel One and 180 seconds after Curry's order to "go to the hospital" on Channel Two. When Bellah's words are used to line up the two channels, Thomas found, the gunshot sounds "occur at the exact instant that John F. Kennedy was assassinated."

How is it, then, that Decker's remarks on Channel One come a full minute after Curry's on Channel Two and yet a half-second after the last gunshot on Channel One?

"It's a misplaced bit of speech," Thomas said in an interview. "An overdub. The recording needle for Channel One probably jumped. You can hear Decker giving a whole set of instructions on Channel Two, but on Channel One, you get only a fragment, '... hold everything secure. ... ' "

According to Thomas, the NAS panel made other mistakes: in calculating the position of the grassy knoll shooter, in fixing the time of that shot and in stating the Channel Two recorder had stopped when it hadn't. In all, Thomas said, the chances of the NAS panel having been right were 1 in 100,000.

House committee experts James Barger, Mark Weiss and Eric Aschkenasy, have always held firm to their findings of a shot from the knoll. Similarly, Ramsey, as chairman of the NAS panel, said last weekend that he was "still fairly confident" of his group's work, but he said he wanted to study the SCIENCE AND JUSTICE article before making further comment. He said he did not recall the Bellah cross talk.

Thomas's article can be found at the following address: (Requires Adobe Acrobat Reader)




(2) Weiss-Aschkenasy analysis.--In mid-September 1978, the committee asked Weiss and Aschkenasy, the acoustical analysts who had reviewed Barger's work, if they could go beyond what Barger had done to determine with greater certainty if there had been a shot from the grassy knoll. Weiss and Aschkenasy conceived an analytical extension of Barger's work that might enable them to refine the probability estimate. (45) They studied Dealey Plaza to determine which structures were most got to have caused the echoes received by the microphone in the 1978 acoustical reconstruction that had recorded the match to the shot from the grassy knoll. They verified and refined their identifications of echo-generating structures by examining the results of the reconstruction. And like BBN, since they were analyzing the arrival time of echoes, they made allowances for the temperature differential, because air temperature affects the speed of sound. (46) Barger then reviewed and verified the identification of echo-generating sources by Weiss and Aschkenasy. (47)

With respect to the other shots, Barger estimated there was an 88 percent chance that impulse pattern one represented a shot from the book depository (based on three matches), 88 percent again for impulse pattern two (three matches) and a 75 percent chance that impulse pattern four represented a shot from the depository (two matches). (43) At the time of his testimony in September 1978, Barger estimated that the probability of all four impulses actually representing gunshots was only 29 percent. (44)

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Once they had identified the echo-generating sources for a shot from the vicinity of the grassy knoll and a microphone located near the point indicated by Barger's tests, it was possible for Weiss and Aschkenasy to predict precisely what impulse sequences (sound fingerprints) would have been created by various specific shooter and microphone locations in 1963. (48) (The major structures in Dealey Plaza in 1978 were located as they had been in 1963.) Weiss and Aschkenasy determined the time of sound travel for a series of sound triangles whose three points were shooter location, microphone location and echo-generating structure location. While the location of the structures would remain constant, the different combinations of shooter and microphone locations would each produce a unique sound travel pattern, or sound fingerprint. (49) Using this procedure, Weiss and Aschkenasy could compare acoustical fingerprints for numerous precise points in the grassy knoll area with the segment identified by Barger on the dispatch tape as possibly reflecting a shot fired from the knoll. (50)

Because Weiss and Aschkenasy could analytically construct what the impulse sequences would be at numerous specific shooter and microphone locations, they decided to look for a match to the 1963 police dispatch tape that correlated to within ±1/1.000 of a second, as opposed to +-6/1.000) of a second, as Barger had done.(51) By looking for a match with such precision, they considerably reduced the possibility that any match they found could have been caused by random or other noise,(52) thus substantially reducing the percentage probability of an invalid match.

Weiss and Aschkenasy initially pinpointed a combination of shooter-microphone locations for which the early impulses in pattern three matched those on the dispatch tape quite well, although later impulses in the pattern did not. Similarly, they found other microphone locations for which later impulses matched those on the dispatch tape, while the earlier ones did not. They then realized that, a microphone mounted on a motorcycle or other vehicle would not have remained stationary during the period it was receiving the echoes. They computed that the entire impulse pattern or sequence of echoes they were analyzing on the dispatch tape occurred over approximately three-tenths of a second, during which time the motorcycle or other vehicle would have, at 11 miles per hour, traveled about five feet. By taking into account the movement of the vehicle. Weiss and Aschkenasy were able to find a sequence of impulses representing a shot from the grassy knoll in the reconstruction that matched both the early and late impulses on the dispatch tape. (53)

Approximately 10 feet from the point on the grassy knoll that was picked as the shooter location in the 1978 reconstruction and four feet from a microphone location which, Barger found, recorded a shot that matched the dispatch tape within +-6/1,000 of a second, Weiss and Aschkenasy found a combination of shooter and microphone locations they needed to solve the problem. It represented the initial position of a microphone that would have received a series of impulses matching those on the dispatch tape to within +-1/1.000 of a second. The microphone would have been mounted on a vehicle that was moving along the motorcade route at 11 miles per hour.

Weiss and Aschkenasy also considered the distortion that a windshield might cause to the sound impulses received by a motorcycle microphone. They reasoned that the noise from the initial muzzle blast of a shot would be somewhat muted on the tape if it traveled through the windshield to the microphone. Test firings conducted under the auspices of the New York City Police Department confirmed this hypothesis. Further, an examination of the dispatch tape reflected similar distortions on shots one, two, and three, when the indicated positions of the motorcycle would have placed the windshield between the shooter and the microphone. On shot four, Weiss and Aschkenasy found no such distortion. (55) The analysts' ability to predict the effect of the windshield on the impulses found on the dispatch tape, and having their predictions confirmed by the tape, indicated further that the microphone was mounted on a motorcycle in Dealey Plaza and that it had transmitted the sounds of the shots fired during the assassination.

Weiss and Aschkenasy examined only the impulse sequence that Barger indicated had come from the grassy knoll. Due to time constraints, they did not analyze the three impulse sequences indicating shots fired from the Texas School Book Depository.

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Since Weiss and Aschkenasy were able to obtain a match to within +-1/1,000 of a second, the probability that such a match could occur by random chance was slight. Specifically, they mathematically computed that, with a certainty factor of 95 percent or better, there was a shot fired at the Presidential limousine from the grassy knoll.(56)

Barger independently reviewed the analysis performed by Weiss and Aschkenasy and concluded that their analytical procedures were correct. (57) Barger and the staff at BBN also confirmed that there was a 95 percent chance that at the time of the assassination a noise as loud as a rifle shot was produced at the grassy knoll. When questioned about what could cause such a noise if it were not a shot, Barger noted it had to be something capable of causing a very loud noise--greater than a single firecracker.(58) Further, given the echo patterns obtained, the noise had to have originated at the very spot behind the picket fence on the grassy knoll that had been identified,(59) indicating that it could not have been a backfire from a motorcycle in the motorcade. (60)

In addition, Barger emphasized, the first part of the sequence of impulses identified as a shot from the grassy knoll was marked by an N-wave, a characteristic impulse caused by a supersonic bullet. (61) The N-wave, also referred to as a supersonic shock wave, travels faster than the noise of the muzzle blast of a gun and therefore arrives at a listening device such as a microphone ahead of the noise of a muzzle blast. The presence of the N-wave was, therefore, a significant additional indication that the third impulse on the police dispatch tape represented gunfire, and, in particular, a supersonic bullet.(62) The weapon may well have been a rifle, since most pistols except for some such as a .44 magnum--fire subsonic bullets. The N-wave was further substantiation for a finding that the third impulse represented a shot fired in the direction of the President. Had the gun been discharged when aimed straight up or down, or away from the motorcade, no N-wave would have appeared. (63) Of the impulse patterns on the dispatch tape that indicated shots from the book depository, those that would be expected to contain an N-wave, given the location of the vehicle's microphone, did so, further corroborating the conclusion that these impulses did represent supersonic bullets. (64)

The motorcycle was traveling 120 feet behind the Presidential limousine when the shots were fired. This put shots one and two from the book depository, as well as shot three from the grassy knoll, in front of the motorcycle windshield.

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When questioned about the probability of the entire third impulse pattern representing a supersonic bullet being fired at the President from the grassy knoll, Barger estimated there was a 20 percent chance that the N-wave, as opposed to the sequence of impulses following it, was actually caused by random noise.(65) Accordingly, the mathematical probability of the entire sequence of impulses actually representing a supersonic bullet was 76 percent, the product of a 95 percent chance that the impulse pattern represented noise as loud as a rifle shot from the grassy knoll times an 80 percent chance that the N-wave was caused by a supersonic bullet. (66)

The committee found no evidence or indication of any other cause of noise as loud as a rifle shot coming from the grassy knoll at the time the impulse sequence was recorded on the dispatch tape, and therefore concluded that the cause was probably a gunshot fired at the motorcade.

Search for a motorcycle.---As the work of Weiss and Aschkenasy produced strong indications of a shot from the grassy knoll, the committee began a search of documentary and photographic evidence to determine if a motorcycle or other vehicle had been in the locations indicated by the acoustical tests.

Earlier in its investigation, the committee had interviewed many Dallas police officers who had ridden in the presidential motorcade, although the purpose of the interviews was not to determine the location of a motorcycle that might have had its radio transmitting switch stuck in the "on" position. Among the officers who were interviewed, one who subsequently testified in a public hearing was H.B. McLain. In his interview on September 26, 1977, McLain said that he had been riding to the left rear of Vice President Johnson's car and that just as he was completing his turn from Main onto Houston Street, he heard what he believed to have been two shots. (67) Sergeant Jimmy Wayne Courson was also interviewed on September 26. 1977. He stated that his assignment in the motorcade was in front of the press bus, approximately six or seven cars to the rear of the presidential limousine, and that as he turned onto Houston Street, he heard three shots about a second apart. (68) Neither officer was asked specifically whether his radio was on channel one or two, or whether his microphone switch might have been stuck in the transmit position.

The committee obtained Dallas Police Department assignment records confirming that McLain and Courson had both been assigned to the left side of the motorcade, (69) and it discovered photographic evidence(70) that Courson was riding to the rear of McLain, and as Courson recalled,(71) he was in the vicinity of the press bus. The available films revealed that throughout the motorcade the spacing of the motorcycles varied, but that McLain was generally several car lengths ahead of Courson and therefore much closer to the presidential and Vice Presidential limousines. (72) No photographs of the precise locations of the two officers at the moment of the assassination were, at that time, found. Photographs taken shortly before the assassination, however, did indicate that McLain was on Houston Street heading toward Elm as the presidential limousine was turning onto Elm in front of the Texas School Book Depository. (73) At the time of the assassina tion, therefore, he would have been in the approximate position of the transmitting microphone, as indicated by the acoustical analysis.

Subsequent to the committee's final vote on its findings, additional photographic evidence of the actions of Officer McLain was received by the committee from Robert Groden, a consultant to the committee. (74) It supported the committee's conclusion with respect to McLain's testimony, but since it was not received until after the vote, it was not relied upon in this report.

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The committee reviewed transcripts of the Dallas police dispatch tapes for both channel one and channel two. It did not find any voice transmissions from McLain on either channel on November 22, 1963. (As noted, it was determined that the shots fired during the assassination were recorded over channel one. If it could have been established that McLain was transmitting over channel two, then the gunfire transmissions could not have come from his motorcycle radio.)

McLain was asked by the committee to come to Washington to testify. He was shown all of the photographic evidence that the committee had assembled, as well as the Dallas police records of the motorcade assignments. McLain testified before the committee on December 29, 1978, that he was assigned to ride on the left side of the motorcade; that since he would slow down at corners, often stopping momentarily, and then speed up during straight stretches, his exact, position in the motorcade varied; and that he was the first motorcycle to the rear of the Vice presidential limousine. (75)

He further stated that he was the officer in the photographs taken of the motorcade on Main and Houston Streets, and that at the time of the assassination he would have been in the approximate position of the open microphone near the corner of Houston and Elm, indicated by the acoustical analysis. (76) He did not recall using his radio during the motorcade nor what channel it was tuned to on that day. (77) He stated it unusually was tuned to channel one. (78) The button on his transmitter receiver, he acknowledged, often got stuck in the "on" position when he was unaware of it, but he did not know if it was stuck during the motorcade. (79)

McLain testified before the committee that he recalled hearing only one shot and that he thereafter heard Chief Curry say to go to the hospital. (80) McLain testified it was possible that he heard the broadcast of Chief Curry (which would have been on channel two) over the speaker of his own radio, or over the speaker of the radio of another motorcycle.(81)

Following the hearing, the committee secured a copy of the daily assignment sheet for motorcycles from the Dallas Police Department and found that McClain had been assigned motorcycle number 352 and call sign 155 on November 22, 1963.(82) Preliminary photographic enhancement of the films taken on Houston and Main Streets indicated that the number on the rear of the motorcycle previously identified as having been ridden by McLain was, in fact, 352. (83)

During his public testimony, McLain also identified photographs of motorcycles on Elm Street (JFK Exhibit F-675) and at Parkland Hospital (JFK Exhibits 674, 676, 677, and 678) as possibly portraying his motorcycle. Of the pictures at Parkland Hospital (JFK Exhibit F-674) apparently indicates that the microphone button was turned to channel one. With respect to the photograph on Elm Street, McLain stated that the other motorcycle in the picture appeared to be ridden by Sergeant Courson. At that time, counsel cautioned that the photographs were being introduced for a limited purpose, since they had not been analyzed by any photographic experts; it was unclear if the cycle in each photograph was that of McLain; and the channel selector, even if it was on channel one, could have been switched after the shots were fired. Preliminary photographic analysis of those pictures conducted by one expert in the time available after the hearing cast doubt upon the accuracy of at least McLain's identification of Courson in Exhibit F-675, and indicated that the channel selector on the motorcycle in Exhibit F-674 may have been on channel two instead of one. because the committee was unable to conduct comprehensive and thorough analyses of those photographs, it did not rely on Exhibits F-674, F-675, F-676, F-677 or F-678 in forming any conclusions.

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The committee recognized that its acoustical analysis first established and then relied on the fact that a Dictabelt had recorded transmissions from a radio with a stuck microphone switch located in Dealey Plaza. The committee realized that the authenticity of the tape and the location of the stuck microphone were both of great importance to the acoustical analysis. Consequently, it sought to verify that the tape in fact contained a broadcast from an open motorcycle microphone in Dealey Plaza during the assassination.

The findings of the acoustics experts may be challenged by raising a variety of questions, questions prompted, for example, by the sound of sirens on the tape,(84) by statements by Officer McLain subsequent to his hearing testimony in which he denied that it was his radio that was transmitting, (85)"by what appears to be the sound of a carillon bell on the tape, (86) and by the apparent absence of crowd noise. The committee carefully considered these questions as they bore on the authenticity of the tape and the location of the stuck microphone.

Approximately 2 minutes after the impulse sequences that, according to the acoustical analysis, represent gunfire, the dispatch tape contains the sound of sirens for approximately 40 seconds. The sirens appear to rise and then recede in intensity, suggesting that the position of the microphone might have been moving closer to and then farther away from the sirens, or that the sirens were approaching the microphone and then moving away from it. (87)

If the sirens were approaching the microphone and then moving away from it, it could be suggested that the motorcycle with the stuck transmitter was stationary on the Stemmons Freeway and not in Dealey Plaza. The sirens would appear to increase and then decrease as some vehicles in the motorcade, with their sirens turned on, drove along the freeway on the way to Parkland Hospital, approaching and then passing by the motorcycle with the stuck microphone. According to a transcript of channel two transmissions, approximately 3 1/2 minutes after the assassination Dallas Police Department dispatcher Gerald D. Henslee stated that an unknown motorcycle on Stemmons Freeway appeared to have its microphone switch stuck open on channel one.(88) The committee interviewed Henslee on August 12, 1978. He told the committee he had assumed the motorcycle was on the freeway from the noise of the sirens. (89) Other Dallas police officers have also speculated that the motorcycle may have been standing near the Trade Mart.

Officer McLain's acknowledged actions subsequent to the assassination might explain the sound of sirens on the tape. McLain was in fact probably on Stemmons Freeway at the time Henslee noted that an unknown motorcycle appeared to have its microphone switch stuck open. McLain himself testified that following the assassination, he sped up to catch the front cars of the motorcade that had entered Stemmons Freeway en route to Parkland Hospital. (90) In any event, it is certain he left the plaza shortly after the assassination. The cars in the motorcade had their sirens on, and this could account for the sound of the sirens increasing as McLain drew closer to them, whether he left Dealey Plaza immediately or shortly after the assassination.

McLain's microphone was so constructed that it would pick up only the siren of the motorcycle on which it was mounted or one of a motorcycle or other vehicle that was not more than 300 feet away.

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Subsequent to his hearing testimony, McLain stated that he believed he turned on his siren as soon as he heard Curry's order to proceed to Parkland Hospital. He said that everyone near him had their sirens on immediately. (91) Should his memory be reliable, the broadcast of the shots during the assassination would not have been over his radio, because the sound of sirens on the tape does not come until approximately 2 minutes later. The committee believed that McLain was in error on the point of his use of his siren. Since those riding in the motorcade near Chief Curry had their sirens on, there may have been no particular need for McLain to turn his on, too. The acoustical analysis pinpointing the location of the microphone, the confirmation of the location of the motorcycle by photographs, his own testimony as to his location, and his slowing his motorcycle as it rounded the corner of Houston and Elm (as had been previously indicated by the acoustical analysis),(92) and the likelihood that McLain did not leave the plaza immediately, but legged behind momentarily after the assassination, led the committee to conclude it was Officer McLain whose radio microphone switch was stuck open.

Further, the committee noted, it would have been highly improbable for a motorcycle on Stemmons Freeway to have received the echo patterns for the four impulses that appear on the dispatch tape. As noted in more detail below, to contend that the microphone was elsewhere carries with it the burden of explaining all that appears on the tape. To be sure, those who argue the microphone was in Dealey Plaza must explain the sounds that argue it was not. Similarly, those who contend it was not in Dealey Plaza must explain the sounds that indicate it was. As Aschkenasy testified, the echo patterns on the tape would only have been received by a microphone located in a physical environment with the same acoustical characteristics as Dealey Plaza. (93) It is extremely unlikely that the echo patterns on the tape, if received from elsewhere, would so closely parallel the echo patterns characteristic of Dealey Plaza.

The tape contains the faint sound of a carillon-like bell about 7 seconds after the last impulse believed to have been a shot, but no such bell was known to have been in the vicinity of Dealey Plaza. Accordingly, the possibility that the motorcycle with the stuck radio transmitter might not have been in Dealey Plaza was considered. The committee found that the radio system used by the Dallas Police Department permitted more than one transmitter to operate at the same time, and this frequently occurred.(94) The motorcycle whose radio transmitted the sound of a bell was apparently not positioned in Dealey Plaza, but this did not mean that the transmissions of gunshots were also from a radio not in Dealey Plaza. The logical explanation was that the dispatch tape contains the transmissions of two or more radios. (95)

The absence of identifiable crowd noise on the tape also might raise questions as to whether the motorcycle with the stuck transmitter was in Dealey Plaza. The lack of recognizable crowd noise, however, may be explained by the transmission characteristics of the microphone.

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Dallas police motorcycle. radios were equipped with a directional microphone and were designed to transmit only very loud sounds. A human voice would transmit only if it originated very close to the front of the mike. The chief objective of this characteristic was to allow a police officer, when speaking directly into the microphone, to be heard over the sound of his motorcycle engine. Background noise, such as that of a crowd, would not exceed the noise level from the much closer motorcycle engine, and it would not be identifiable on a tape of the radio transmission. The sound of a rifle shot is so pronounced, however, that it would be picked up even if it originated considerably farther away from the microphone than other less intense noise sources, such crowd. (96)

(c) Other evidence with respect to the shots

To address further the question of whether the dispatch tape contained sounds from a microphone in Dealey Plaza with a stuck transmitting switch, the committee reviewed independent evidence. It reasoned that if the timing, number and location of the shooters, as shown on the tape, were corroborated or independently substantiated in whole or in part by other scientific or physical evidence--that is, the Zapruder film, findings of the forensic pathology and firearms panels, the neutron activation analysis and the trajectory analysis--the validity of the acoustical analysis and the authenticity of the tape could be established. Conversely, any fundamental inconsistency in the evidence would undermine the analysis and the authenticity of the tape.

The tape and acoustical analysis indicated that, in addition to the shot from the knoll, there were three shots fired at President Kennedy from the Texas School Book Depository. This aspect of the analysis was corroborated or independently substantiated by three cartridge cases found on the sixth floor of the Texas School Book Depository on November 22, 1963, cartridge cases that had been fired in Oswald's rifle,(97) along with other evidence related to the number of shots fired from Oswald's rifle. This corroboration was considered significant by the committee, since it tended to prove that the tape did indeed record the sounds of shots during the assassination.

Further corroboration or substantiation was sought by correlating the Zapruder film to the acoustical tape. The Zapruder film contains visual evidence that two shots struck the occupants of the Presidential limousine.(98) The committee attempted to correlate the observable reactions of President Kennedy and Governor Connally in the film to the time spacing of the four impulses found in the recording of the channel one transmission. The correlation between the film and the recording however, could only be approximate because it was based on the estimated real-time characteristics of the recording (calculated from the frequent time annotations made by the dispatcher) (99) and the average running time of the film (between 18.0 and 18.5, or an average of 18.3 frames per second).


ABOUT THE AUTHOR: Michael T. Griffith holds a Master’s degree in Theology from The Catholic Distance University, a Graduate Certificate in Ancient and Classical History from American Military University, a Bachelor’s degree in Liberal Arts from Excelsior College, and two Associate in Applied Science degrees from the Community College of the Air Force.  He also holds an Advanced Certificate of Civil War Studies and a Certificate of Civil War Studies from Carroll College.  He is a graduate in Arabic and Hebrew of the Defense Language Institute in Monterey, California, and of the U.S. Air Force Technical Training School in San Angelo, Texas.  In addition, he has completed Advanced Hebrew programs atHaifa University in Israel and at the Spiro Institute in London, England.  He is the author of five books on Mormonism and ancient texts, including How Firm A Foundation, A Ready Reply, and One Lord, One Faith.  He is also the author of a book on the JFK assassination titled Compelling Evidence (JFK Lancer, 1996).


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