REBUTTAL OF THE HSCA’S PHOTOGRAPHIC EVIDENCE OFFERED IN SUPPORT OF THE COMMITTEE’S ACOUSTIC EVIDENCE OF CONSPIRACY
On September 11, 1978, Dr. James E. Barger told the HSCA in public hearings that the acoustic tests were designed “to see if [the Dallas police tape] was statistically likely to have contained the sounds of gunfire,”  and that the results he obtained were “a potential corroborating force toward other evidence.”  In essence, it was up to the HSCA to find additional evidence that either confirmed or refuted the acoustic tests which predicted that a motorcycle with an open microphone was transmitting the sounds of gunfire from a location 120 feet (plus or minus 9 feet) behind the President’s limousine. 
On December 29, 1978, just 5 days before the HSCA’s investigation was scheduled to expire, the committee met for one final day of televised public hearings. It was during this public session that the HSCA first offered photographic evidence to support the validity of their acoustic evidence of conspiracy.
In his opening remarks, HSCA Chief Counsel G. Robert Blakey stressed the importance of verifying Barger’s work photographically, “If it could be proved that no motorcycle was in the predicted location at the time of the shots, then serious doubt would be raised about the reliability of the acoustics project.”  What Blakey should have said, of course, was that the acoustics evidence would be destroyed by such proof. Barger said as much in a 2001 email exchange, writing, “…if it can be shown that there was no vehicle or person with a police radio near the trajectory where I found it to be, then, that is impeaching evidence.” 
The HSCA presented evidence that only one motorcycle officer was in a position to transmit the sounds of the shooting – Officer H.B. McLain. It was McLain, they concluded, who transmitted the sounds of “gunfire” from a location approximately 120 feet behind the President’s limousine. In their final report, the HSCA offered three amateur film sequences to support their conclusions.
The DCA Film
One sequence, from the Dallas Cinema Associates (DCA) film “President Kennedy’s Final Hour,” shows McLain traveling on Main Street a few blocks before reaching Dealey Plaza and merely establishes that McLain was riding approximately 200 feet behind the President’s limousine about one minute before the shooting.  [Exhibit 56]
The Hughes Film
The second sequence, from an amateur film by Robert Hughes, shows McLain turning onto Houston Street shortly after the presidential limousine had turned onto Elm Street, one block ahead of McLain.  [Exhibit 57] According to the HSCA, the Hughes film showed McLain riding “several car lengths behind the Presidential limousine as it turned in front of the Texas School Book Depository...the place that the acoustics project suggested [the motorcycle] would be.”  The actual distance was over 200 feet.
Unfortunately for the HSCA, the Hughes film doesn’t actually show McLain in the position predicted by their acoustic analysis. The crucial sequence ends just as McLain reaches the crosswalk at Main and Houston, approximately 170 feet from the committee’s first shot position and more than 200 feet behind the presidential limousine. [See Exhibit 4]
Failing to perform any further analysis of the Hughes film sequence to determine its relationship to the shooting, the HSCA was left to draw the rather vague conclusion that McLain “would have been in the approximate position of the transmitting microphone, as indicated by the acoustical analysis.” 
One obvious problem with the committee’s conclusion was how McLain managed to gain 80 feet on the limousine – putting him 120 feet behind the limousine as required by the acoustic evidence – before he reached the first shot position. In public hearings, Dr. Barger testified that McLain only had to “gain a bit on the presidential limousine as he came [up] Houston,” suggesting that the natural accordion-like motion of the motorcade (i.e., the tendency for the procession to accelerate and stretch out over straight portions of the route, then slow and bunch up at each turn) would have allowed McLain to gain the required 80 feet on the presidential limousine as it slowly made its turned onto Elm Street. 
Yet, Barger’s explanation is demonstratively false. The Hughes film shows that the presidential limousine had already completed its turn onto Elm Street and begun to accelerate before McLain turned north onto Houston, eliminating the possibility of McLain gaining on the limousine in the manner Barger described. [Exhibit 58]
In addition, Barger himself testified that the sounds of the motorcycle engine on the acoustic recording remained constant – neither accelerating nor decelerating – until just 3 seconds before the first shot, when the engine sounds appear to slow considerably.  In essence, the recording itself is evidence that McLain couldn’t have accelerated to close the distance between his motorcycle and the presidential limousine in the way that Barger claimed.
The Dorman Film
In early 1979, just as the committee’s final report was about to go to press, the HSCA was presented with a third amateur film sequence by conspiracy theorist Robert Groden who claimed to have discovered photographic proof that McLain was in fact at the location and time specified by the acoustic experts. While the HSCA claimed not to have reviewed Groden’s work, they did report that Groden’s photographic exhibits “supported the committee’s conclusion.” 
Groden’s photographic proof turned out to be the fifth sequence of an amateur film made by Mrs. Elsie Dorman, which depicts a motorcycle escort arriving at the corner of Elm and Houston. [Exhibit 59] Groden claimed that the motorcycle escort was H.B. McLain and that the sequence showed him arriving at the Elm and Houston corner at the time of the first shot – just as the acoustic evidence had predicted.
While the Dorman sequence does in fact depict McLain’s arrival at the Elm and Houston intersection, Groden’s assertion that the Dorman sequence synchronizes to the time of the assassination shots is demonstratively false.
H.B. McLain in the Dorman Film
Three facts support the belief that the motorcycle officer in the Dorman film is H.B. McLain. First, the motorcycle officer in the Dorman film is seen riding on the left side of motorcade between Camera Car 3 and Congressional Car 1 – the same relative position occupied by McLain throughout the entire motorcade  and the precise position occupied by McLain twelve seconds earlier, as depicted in the Hughes film. [Exhibit 60]
Second, the motorcycle officer in the Dorman film has a white object attached to the inside lower-left corner of his windshield. A similar white object is visible on McLain’s motorcycle twelve seconds earlier, as depicted in the Hughes film. [Exhibit 61]
McLain testified that the white object was his paper work which he kept fastened to the inside of the motorcycle’s windshield with two clip holders. This was one of several identifying characteristics which allowed McLain to identify his motorcycle from others used by the police department.  High quality photographs taken before and after the assassination show this unique feature of McLain’s motorcycle. [Exhibit 62]
Third, the trajectory and speed of the motorcycle officer in the Dorman film is consistent with the projected trajectory and speed of McLain’s motorcycle, as depicted in the Hughes film.
To determine Officer McLain’s trajectory and speed as seen in the Hughes film, a computer model of McLain’s motorcycle was positioned to match Hughes frame H632 (the second frame in which McLain appears) by noting the motorcycle’s relationship to a line-of-sight drawn between Hughes’ camera and the windows on the west wall of the Dallas County Courthouse building. A computer model of the motorcycle was also positioned to match Hughes frame H648 (the last frame in which McLain appears) by noting the motorcycle’s relationship to lines-of-sight drawn between Hughes’ camera and the northwest and southwest corners of the Dal-Tex Building. [Exhibit 63] The distance between these two positions (Hughes frames H632-H648) was measured at 18.79 feet. McLain traversed this distance over the course of 16 frames. Dividing the speed of the Hughes camera (18.3 frames/second) into the frame count yields a time of 0.874 seconds. This calculates to a speed of 21.49 feet/second (14.7 mph) as McLain turns the corner from Main onto Houston Street. [Exhibit 64]
To fix the trajectory and speed of the motorcycle officer seen in the Dorman film, multiple Dorman frames were used to create a mosaic image, which illustrated the precise location of the motorcycle officer at Dorman frames D456 (the first frame in which the motorcyclist appears) and D496 (the last frame in which he appears). A line-of-sight was projected from Dorman’s point-of-view, through both motorcycle positions, to the Dallas County Courthouse Building visible in the background. [Exhibit 65] These lines-of-sight were then transferred to a computer model of Dealey Plaza. Computer models of a motorcycle were also matched to the locations shown. The distance between these two positions (Dorman frames D456-D496) was measured at 28 feet. The motorcyclist traversed this distance over the course of 40 frames. Dividing the speed of the Dorman camera (16.8 frames/second) into the frame count yields a time of 2.38 seconds. This calculates to a speed of 11.77 feet/second
(8.0 mph). [Exhibit 66]
The distance between McLain’s position at Hughes frame H648 and the motorcyclist’s position at Dorman D456 was measured at 159.5 feet. Since Hughes frame H648 is the equivalent of Zapruder frame Z150 and Dorman frame D456 is the equivalent of Zapruder frame Z365 [See The Wiegman Film], then a period of 11.75 seconds (Z365 – 150 = 215 ÷ 18.3 = 11.75 sec) is known to have elapsed between McLain’s last appearance in the Hughes film and the motorcycle officer’s appearance in the Dorman film. If McLain continues north on Houston Street at an average speed of 13.58 feet/second (9.3 mph), the approximate speed of the motorcade, he will traverse 159.5 feet in 11.75 seconds and arrive at the corner of Elm and Houston at the time depicted in the Dorman film. [Exhibit 67]
The unique identifying characteristics of McLain’s motorcycle, his relative position in the motorcade procession on Houston Street as depicted in both the Hughes and Dorman films, and the consistency of his speed and trajectory in the Hughes film with that of the motorcyclist in the Dorman film is nearly conclusive evidence that the motorcycle officer in the Dorman film is in fact H.B. McLain.
Synchronizing the Dorman and Zapruder Films
The Dorman film sequence depicting McLain’s arrival at the Elm and Houston intersection does not, however, synchronize to the time of the shooting as Groden claimed, but rather synchronizes to a point after the shooting had ended. This is demonstratively proven by examining details visible in the Dorman sequence immediately preceding the one depicting Officer McLain.
A stabilized portion of the fourth sequence of the Dorman film (D345-D355) shows amateur photographer Hugh Betzner Jr., lowering his camera after taking a photograph of the President’s car. The photograph was taken at the equivalent of Zapruder frame Z186.  [Exhibit 68] In the margins of the Zapruder film, between frames Z195 and Z206, Betzner is also visible lowering his camera exactly as he does in the Dorman film. [Exhibit 69] This action provides a synchronization point.
Everything that follows this moment in the Dorman film must occur after Zapruder frame Z206 – in other words, after the shooting began.
An examination of the Dorman film shows that there is a brief camera stop after this sequence and then Mrs. Dorman resumes filming. When Sequence 5 of the Dorman film begins, six continuous seconds elapse before Officer McLain appears at the corner.
Consequently, McLain’s arrival at the corner of Elm and Houston is not at the time of the first shot – as Groden claimed, and the acoustic evidence dictates – but at least 8 seconds after the shooting began, or, for all practical purposes, after the shooting was over.
The precise relationship between McLain’s arrival at the corner of Elm and Houston as depicted in Dorman sequence D456-D496, and the shooting as depicted in the Zapruder film can be determined by synchronizing the Dorman and Zapruder films using the 16mm news film shot by Dave Wiegman, Jr.
The Wiegman Film
Dave Wiegman was an NBC cameraman riding in Camera Car 1, the tenth automobile in the motorcade. When the shooting began, Wiegman turned on his 16mm news camera, which ran at 24 frames-per-second, jumped from the car in front of the Texas School Book Depository and ran down toward the north pergola.
A computer-assisted geometric analysis of both the Wiegman and Zapruder films demonstrates that Wiegman frame W265, depicting the presidential limousine approaching the Triple Underpass, is the equivalent of Zapruder frame Z447. This was determined by plotting a line-of-sight on a computer model of Dealey Plaza between Wiegman’s position at Wiegman frame W265 and the U.S. flag mounted on the right-front fender of the presidential limousine visible in the background of that same frame. A second line-of-sight was then plotted between Zapruder’s position and the lamppost on the north side of Elm Street nearest to the limousine’s position, as depicted in the Wiegman
film. [Exhibit 70] The Zapruder film was then studied to determine the frame at which the presidential limousine matched the location indicated by the two lines-of-sight. The Zapruder frame matching the position of the limousine at Wiegman frame W265 is Zapruder frame Z447. [Exhibit 71]
To determine the relationship of the Dorman film to the Wiegman film (and thus, its relationship to the Zapruder film), an examination was made of the movements of Mayor Earle Cabell’s car, the eighth automobile in the motorcade, which appears in both films.
Using the Wiegman and Dorman films, as well as measurements obtained from a computer model of Dealey Plaza, it was possible to triangulate the trajectory and speed of Mayor Cabell’s car as it passed the Texas School Book Depository, and thus, synchronize the two films. The results show that:
(a) Mayor Cabell’s car at Wiegman frame W015 was determined to be 19.2 feet from its position at Dorman frame D376.
Mayor Cabell’s car was a 1963 Mercury Comet which had an overall length of 194.8 inches (16.2 feet).  A computer model of Mayor Cabell’s car was positioned to match Wiegman frame W015 by noting the vehicle’s relationship to a line-of-sight drawn between Wiegman’s camera and the western edge of the fourth window alcove located west of the entrance to the Texas School Book Depository. A computer model of Mayor Cabell’s car was also positioned to match a composite version of Dorman frame D376  by noting the vehicle’s relationship to a line-of-sight drawn between Dorman’s camera and the curved concrete wall rimming the reflecting pool on the south side of Elm Street. The left rear window of Mayor Cabell’s car lies along this line-of-sight. The distance between these two positions (rear bumper-to-rear bumper) was measured at 19.2 feet. [Exhibits 72 & 73]
(b) A computer model of the position of Mayor Cabell’s car at Dorman frame D376 and D390 shows that it traverses a distance of 13.69 feet.
A computer model of Mayor Cabell’s car was positioned to match a composite version of Dorman frame D376 as described above. [See, (a)] A computer model of Mayor Cabell’s car was also positioned to match a composite version of Dorman frame D390 by noting the vehicle’s relationship to a line-of-sight drawn between Dorman’s camera and the concrete tower located west of the reflecting pool on the south side of Elm Street. The left rear window of Mayor Cabell’s car lies along this line-of-sight. The distance between these two positions (left-rear window to left-rear window) was measured at 13.69 feet. [Exhibit 74]
(c) Mayor Cabell’s car speed between Dorman frames D376-D390 was calculated to be 16.44 feet/second (11.2 mph).
During the period defined by Dorman frames D376-D390, Mayor Cabell’s car traverses a distance of 13.69 feet in 14 frames. Dividing the speed of the Dorman camera (16.8 frames/second) into the frame count yields a time of 0.833 seconds. This calculates to a speed of 16.44 feet/second
(11.2 mph). [Exhibit 75]
(d) Mayor Cabell’s car would have traversed the 19.2 feet between Wiegman frame W015 and Dorman frame D376 in 1.17 seconds traveling at an estimated speed of 16.44 feet/second (11.2 mph).
Dividing the distance of 19.2 feet by the estimated speed of 16.44 feet/second (11.2 mph) yields a time period of 1.17 seconds. In conclusion, the four calculations above demonstrate that Mayor Cabell’s car would have traversed the 19.2-foot distance between its known positions at Wiegman frame W015 and Dorman frame D376 in 1.17 seconds. This time period is equal to 28 Wiegman frames (1.17 X 24fps = 28). Consequently, Dorman frame D376 is the equivalent of Wiegman frame W043 (W015 + 28 = W043). [Exhibit 76]
Since Wiegman frame W265 is the equivalent of Zapruder frame Z447, Wiegman-Dorman frame W043-D376 is the equivalent of Zapruder frame Z278. This was determined by taking the 222 total frame count between Wiegman W043 and W265 and dividing by 24 frames-per-second (the frame rate of Wiegman’s camera) which yields a time period of 9.25 seconds. This time period equates to 169 Zapruder frames (9.25 x 18.3 = 169). Subtracting 169 frames from Zapruder frame Z447 yields Zapruder frame Z278 (447 – 169 = 278). Therefore, Wiegman-Dorman frame W043-D376 is the equivalent of Zapruder frame Z278.
We can now compute the relationship between McLain’s arrival at the corner of Elm and Houston, as depicted in Dorman sequence D456-D496, and the Zapruder film. The total frame count between Dorman frame D376 and D456 is 80 frames. Dividing the frame count by the Dorman camera speed yields a time period of 4.76 seconds (80 ÷ 16.8 = 4.76). This time period equates to 87 Zapruder frames (4.76 x 18.3 = 87). Adding 87 frames to Zapruder frame Z278 (the equivalent of Dorman frame D376) equals Zapruder frame Z365. Therefore, Dorman frame D456, the first frame of the sequence depicting McLain’s arrival at Elm and Houston, is the equivalent of Zapruder frame Z365. The final frame of the McLain arrival sequence, Dorman frame D496, likewise equates to Zapruder
frame Z409. 
In conclusion, the Dorman sequence D456-D496, depicting McLain’s arrival at the corner of Elm and Houston, synchronizes to the period 2.84 to 5.25 seconds after the last shot; the equivalent of Zapruder frames Z365 to Z409. [Exhibit 77] Consequently, Robert Groden’s claim that the Dorman sequence showed McLain arriving at the Elm and Houston corner at the time of the first shot – just as the acoustic evidence had predicted – is demonstratively false.
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