A Dictabelt recording from a motorcycle police officer's radio microphone stuck in the open position became a key piece of evidence cited by the House Select Committee on Assassinations (HSCA) in their conclusion that there was a conspiracy behind the assassination of John F. Kennedy on November 22, 1963. Made on a common Dictaphone-brand dictation machine that recorded sound in grooves pressed into a thin vinyl-plastic belt, the recording gained prominence among Kennedy assassination conspiracy theorists following the HSCA's 1978 conclusion, based in part on this evidence, that there was a "high probability" that Lee Harvey Oswald did not act alone and that the Kennedy assassination was the result of a conspiracy.
The recording was made from Dallas Police Radio Channel 1, which carried routine police radio traffic. Channel 2 was reserved for special events such as the presidential motorcade. The open-microphone portion of the recording lasts 5.5 minutes and begins at about 12:29 p.m. local time, a minute before the assassination. In addition, there are two earlier open-mic portions of the recording: one at 12:24 p.m. (4.5 seconds) and the other at 12:28 p.m. (17 seconds). J. C. Bowles, The Kennedy Assassination Tapes: A Rebuttal to the Acoustical Evidence Theory , 1979.Warren Commission Hearings, Commission Exhibit 705, Radio log of channel 1 of the Dallas Police Department for November 22, 1963 , vol. 17, p. 395."Reexamination of Acoustic Evidence in the Kennedy Assassination," Committee on Ballistic Acoustics, National Research Council, SCIENCE, 8 October 1982, "Signal Processing Analysis of the Kennedy Assassination Tapes," R.C. Agarwal, R. L. Garwin, and B. L. Lewis, IBM T. J. Watson Research Center, Verbal time stamps were made periodically by the police radio dispatcher and can be heard on the recording.Warren Commission Hearings, vol. XVII, pp. 390-455, CE 705, Transcription of all radio transmissions from Dallas police channel 1 and channel 2 from 12:20 p.m. to 6:00 p.m., Nov. 22, 1963 .
House Select Committee on Assassinations In December 1978, the House Select Committee on Assassinations (HSCA) had prepared a draft of its final report, concluding that Lee Harvey Oswald had acted alone in the assassination. However, after evidence from the Dictabelt recording was made available, the HSCA quickly reversed its conclusion and declared that a second gunman had fired the third of four shots heard. In a January 5, 1980, interview with journalist Earl Golz, HSCA chief counsel G. Robert Blakey later said: "If the acoustics come out that we made a mistake somewhere, I think that would end it [the multiple-shooter theory]." Despite serious criticism of the scientific evidence and the HSCA's conclusions, speculation regarding both the Dictabelt and the possibility of a second gunman persisted.
Investigators compared "impulse patterns" (suspected gunshots and associated echos) on the Dictabelt to 1978 test recordings of Carcano rifles fired in Dealey Plaza from the sixth floor of the Texas School Book Depository and from a stockade fence on the grassy knoll forward and to the right of the location of the presidential limousine. On this basis, the acoustics firm of Bolt, Beranek and Newman (BBN) concluded that impulse patterns 1, 2, and 4 were shots fired from the Depository, and that there was a 50% chance that impulse pattern 3 was a shot fired from the grassy knoll. Acoustics analysts Mark Weiss and Ernest Aschkenasy of Queens College reviewed the BBN data and concluded that "with the probability of 95% or better, there was indeed a shot fired from the grassy knoll."
Dr. James E. Barger of BBN testified to the HSCA that his statistical analysis of the impulse patterns captured on the Dallas police recordings showed that the motorcycle with the open microphone was about "120 to 138 feet" behind the presidential limousine at the time the first shot was fired.Testimony of Dr. James Barger, 5 HSCA 650 . When the HSCA asked Weiss about the location of the motorcycle with the open microphone—"Would you consider that to be an essential ingredient in the ultimate conclusion of your analysis?"— Weiss answered, "It is an essential component of it, because, if you do not put the motorcycle in the place that it is —the initial point of where it was receiving the [sound of the gunfire]—, and if you do not move it at the velocity at which it is being moved on paper in this re-creation, you do not get a good, tight pattern that compares very well with the observed impulses on the police tape recording."HSCA Record 180-10120-10025, HSCA Committee Briefing, December 18, 1978, pp. 22–23.
Using an amateur film shot of the motorcade,Taken by Robert Hughes. the HSCA concluded that the recording originated from the motorcycle of police officer H. B. McLain, who later testified before the committee that his microphone was often stuck in the open position. McLain did not hear the actual recording until after his testimony, and upon hearing it, he adamantly denied that the recording came from his motorcycle. He said that the other sounds on the recording did not match any of his movements.H.B. McLain interviewed by Vincent Bugliosi, Reclaiming History: The Assassination of President John F. Kennedy, 2007, , endnotes pp. 177 & 203.
Sirens are not heard on the recording until over two minutes after what is supposed to be the sound of the shooting, even though McLain accompanied the motorcade to Parkland Hospital immediately after the shooting with sirens blaring the whole time. When the sirens are heard on the Dictabelt recording, they rise and recede in pitch (i.e., the Doppler effect) and volume, as if they are passing by, rather than being recorded from a motorcycle accompanying the motorcade on the drive to the hospital. McLain also said that the engine sound was clearly from a three-wheeled motorcycle, not the two-wheeler that he drove. "There's no comparison to the two sounds," he said.
Other audio discrepancies also exist. Crowd noise is not heard on the Dictabelt recording, despite the sounds generated from the many onlookers along Dallas's Main Street and in Dealey Plaza (crowd noises can be heard on at least ten channel-2 transmissions from the motorcade). Someone is heard whistling a tune about a minute after the assassination.James C. Bowles, The Kennedy Assassination Tapes: A Rebuttal to the Acoustical Evidence Theory, Transcripts of Dallas Police Department Radio Communications, November 22, 1963, Annotated . No one actually heard gunshots on the recording.Vincent Bugliosi, Reclaiming History: The Assassination of President John F. Kennedy, 2007, , p. 380.Larry M. Sturdivan, The JFK Myths: A Scientific Investigation of the Kennedy Assassination, 2005, p. 72,
Some have argued that the only evidence that HSCA had for a second shooter was the Dictabelt sound recording.Vincent Bugliosi, Reclaiming History: The Assassination of President John F. Kennedy, 2007, , endnotes pp. 202-3, citing the HSCA report, p. 84."The acoustic evidence that was the sole objective, scientific support for the existence of a conspiracy in the HSCA investigation was debunked.", Sturdivan, 2005, p. 77"The more than six-hundred page draft was put aside, and a majority of the [HSCA] committee approved a preliminary nine-page "Summary of Findings and Recommendations" that concluded, based solely on the flawed acoustics findings, that there was a conspiracy to kill JFK involving a second gunman." ... "Blakely later told a journalist [Earl Golz], 'If the acoustics come out that we made a mistake somewhere, I think that would be the end of it.' " Posner, 1993, p. 457 However the committee's Chief Counsel G. Robert Blakey wrote that this was a "myth" and the recording "played a major, though not determinative, role in favor of conspiracy". Four of the twelve HSCA members dissented to the HSCA's conclusion of conspiracy based on the acoustic findings, and a fifth thought a further study of the acoustic evidence was "necessary".HSCA Report pp. 483–499 , 503–509 . Dissenting members of the committee included Congressmen Samuel L. Devine, Robert W. Edgar, and Harold S. Sawyer. Responding to a question asking how he would handle the Committee's report if he were at the Justice Department, Sawyer replied: "I'd file it in a circular file."
Criticism Richard E. Sprague, an expert on photographic evidence of the assassination and a consultant to the HSCA, noted that the amateur film the HSCA relied on showed that there was no motorcycle between those riding alongside the rear of the presidential limousine and H.B. McLain's motorcycle, and that other filmsTaken by Elsie Dorman, Mal Couch, and Dave Wiegman. showed McLain's motorcycle was actually 250 feet behind the presidential limousine when the first shot was fired, not 120 to 138 feet. There was also no motorcycle anywhere near the target area.Letter, Richard E. Sprague to Harold S. Sawyer, March 3, 1979, pp. 1–2, Sprague Collection, National Archives.
Adult magazine Gallery published a pull-out laminated cardboard recording, like those on the back of Cereal boxes, of the Dictabelt recording in its July 1979 issue.Posner, Gerald. Case Closed, 1993, p. 241 Assassination researcher Steve Barber repeatedly listened to that recording and heard the words "Hold everything secure until the homicide and other investigators can get there" at the point where the HSCA had concluded the assassination shots were recorded. However, those words were spoken by Sheriff Bill Decker about 90 seconds after the assassination, so the shots could not be when the HSCA claimed.Sheriff Decker's words were broadcast on channel 2, but they were apparently picked up by a microphone stuck open on channel 1 from the loudspeaker of a nearby police vehicle.
The FBI's Technical Services Division studied the acoustical data and issued a report on December 1, 1980 (dated November 19, 1980). The FBI report concluded that the HSCA failed to prove that there were gunshots on the recording and also failed to prove that the recording was made in Dealey Plaza. In fact, using the techniques of the previous investigators, the FBI matched a gunshot recorded in Greensboro, NC in 1979 with the sound that was supposedly a shot from the grassy knoll – purportedly suggesting that the initial investigation's methods were invalid.Vincent Bugliosi, Reclaiming History: The Assassination of President John F. Kennedy, 2007, , endnotes p. 199.
National Academy of Sciences After the FBI disputed the validity of the acoustic evidence, the Justice Department paid for a review by the National Academy of Sciences, an organization operating with a Title 36 congressional charter.
On May 14, 1982, the panel of experts chaired by Harvard University's Norman Ramsey, released the results of their study. The NAS panel unanimously concluded that: The acoustic analyses do not demonstrate that there was a grassy knoll shot, and in particular there is no acoustic basis for the claim of 95% probability of such a shot.The acoustic impulses attributed to gunshots were recorded about one minute after the President had been shot and the motorcade had been instructed to go to the hospital.Therefore, reliable acoustic data do not support a conclusion that there was a second gunman."
According to Ramsey, noises on the Dictabelt were "probably static". Louis Stokes, a member of the United States House of Representatives who chaired the HSCA, commented that the report "raised new and serious questions about our conclusions that need to be resolved."