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A Dictabelt recording from a microphone stuck in the open position on a motorcycle police officer's radio in the vicinity of the assassination of John F. Kennedy in Dallas, Texas on November 22, 1963, has been used as evidence related to the assassination. The recording, made on a common Dictaphone dictation machine that recorded sounds in grooves pressed into a thin plastic belt, gained prominence among Kennedy assassination conspiracy theorists starting in 1978, when it was the only piece of evidence that prompted the House Select Committee on Assassinations (HSCA) to conclude that there was a "high probability" that Lee Harvey Oswald did not act alone and the Kennedy assassination was the result of a conspiracy. Later scientific examination discredited this interpretation of the evidence. 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 about 12:29 p.m. local time, about a minute before the assassination at 12:30 p.m.〔In addition, there are two earlier open-mic portions of the recording, at 12:24 p.m. (4.5 seconds) and 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 as the assassin. 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. G. Robert Blakey, chief counsel of the HSCA, later said, "If the acoustics come out that we made a mistake somewhere, I think that would end it." Despite serious criticism of the scientific evidence and the HSCA's conclusions, speculation regarding 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 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 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 Bolt, Beranek and Newman, 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 approximately "120 to 138 feet" behind the presidential limousine at the time of the first shot.〔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 (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.〕 The HSCA, using an amateur film shot of the motorcade,〔Taken by Robert Hughes.〕 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. However, McLain did not hear the actual recording until after his testimony, and upon hearing it he adamantly denied that the recording originated from his motorcycle. He said that the other sounds on the recording did not match his movements. Sirens are not heard on the recording until more than two minutes after what is supposed to be the sound of the shooting; however, McLain accompanied the motorcade to Parkland Hospital immediately after the shooting, with sirens blaring the entire time. When the sirens are heard on the Dictabelt recording, they rise and recede in pitch (the Doppler effect) and volume, as if passing by. 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."〔H.B. McLain interviewed by Vincent Bugliosi, ''Reclaiming History: The Assassination of President John F. Kennedy'', 2007, ISBN 978-0-393-04525-3, endnotes pp. 177 & 203.〕 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, ISBN 978-0-393-04525-3, p. 380.〕〔Larry M. Sturdivan, ''The JFK Myths: A Scientific Investigation of the Kennedy Assassination'', 2005, p. 72, ISBN 978-1-55778-847-4〕 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, ISBN 978-0-393-04525-3, 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 () 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 (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〕 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." 〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「John F. Kennedy assassination Dictabelt recording」の詳細全文を読む スポンサード リンク
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