THE
HSCA's ACOUSTICAL EVIDENCE:
PROOF
OF A SECOND GUNMAN?
Michael T. Griffith
2003
@All Rights Reserved
Third 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
which 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
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
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
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
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
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
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
The tape is an important piece of evidence
because it could 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
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
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
Film of the
motorcade on
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
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
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).
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
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
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. (
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 conspiracists
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
which 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
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
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
. . . examination
of the correlations between the test shots and the sounds on the
In summary, there is some evidence
supporting the Committee's acoustical findings, but there is also evidence
against them. Further study of the dictabelt tape must be done in order to
determine for an absolute certainty 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.)
NOTE: A new 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 address: www.forensic-science-society.org.uk/Thomas.pdf (Requires Adobe Acrobat Reader). See Appendix A at
the end of this article for a summary of Thomas's article.
Also, in a recent lecture on the acoustical
evidence, Dr. Thomas presented evidence that McClain's mike was the mike that
recorded the sound impulses. In addition, Dr. Thomas answered various attacks
on the acoustical evidence, including the rebuttal done by an FBI forensics
expert. The text of Dr. Thomas's lecture is available online: Hear No Evil: The Acoustical Evidence in the Kennedy
Assassination.
----------------------------------------------------------------
BIBLIOGRAPHY
Blakey, G. Robert and Richard Billings,
FATAL HOUR: THE ASSASSINATION OF PRESIDENT KENNEDY BY ORGANIZED CRIME,
Cornwell, Gary, REAL ANSWERS: THE JOHN F.
KENNEDY ASSASSINATION,
Groden, Robert and Harrison Edward
Livingstone, HIGH TREASON: THE ASSASSINATION OF PRESIDENT KENNEDY AND THE NEW
EVIDENCE OF CONSPIRACY,
Livingstone, Harrison Edward, KILLING THE
TRUTH: DECEIT AND DECEPTION IN THE JFK CASE,
Marrs, Jim, CROSSFIRE: THE PLOT THAT KILLED
KENNEDY,
Marsh, W. Anthony, "The Ramsey
Report," DATELINE:
Posner, Gerald, CASE CLOSED: LEE HARVEY
OSWALD AND THE ASSASSINATION OF JFK,
Scally, Christopher, "SO NEAR . . . AND
YET SO FAR": THE HOUSE SELECT COMMITTEE ON ASSASSINATIONS' INVESTIGATION
INTO THE MURDER OF PRESIDENT JOHN F. KENNEDY,
Scheim, David S., THE MAFIA KILLED PRESIDENT
KENNEDY,
Smith, Matthew, JFK: THE SECOND PLOT,
Trask, Richard, PICTURES OF THE PAIN:
PHOTOGRAPHY AND THE ASSASSINATION OF PRESIDENT KENNEDY,
APPENDIX A
"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
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
A new, peer-reviewed article in Science
and Justice, a quarterly publication of
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.
HOUSE INVESTIGATOR SEES VINDICATION
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
The Warren Commission had concluded in 1964 that only three shots, all from
behind, all from Oswald's rifle, were fired in
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.
MISALIGNED AUDIO CHANNELS
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
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."
SEVERAL ERRORS CITED
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
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:
http://www.forensic-science-society.org.uk/Thomas.pdf (Requires Adobe Acrobat Reader)
Visit THE WASHINGTON POST online at http://www.washingtonpost.com/.
APPENDIX B
EXTRACT FROM THE HSCA REPORT (pp. 72-79):
(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
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
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
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
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
McLain was asked by the committee to come to
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
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
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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
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
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
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
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
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
The absence of identifiable crowd noise on the tape also might raise
questions as to whether the motorcycle with the stuck transmitter was in
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(c) Other evidence with respect to the shots
To address further the question of whether the dispatch tape contained
sounds from a microphone in
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).
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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