At the time of the assassination of President Kennedy, the Dallas police recorded sounds from an open microphone; these sounds have been previously analyzed by two research groups at the request of the House Select Committee on Assassinations. Both groups concluded with 95% probability that the recordings contained acoustic impulses which provide evidence for the existence of a shot from the grassy knoll area of Dealey Plaza. On the basis of these results and since shots definitely were fired from the Texas School Book Depository, the House Committee concluded that "scientific acoustical evidence establishes a high probability that two gunmen fired at President John F. Kennedy."
Report of the Committee on Ballistic Acoustics studied these reports and the Dallas Police recordings on which they are based. This book reviews the methodology employed in the evaluations of the recorded acoustic data and of the conclusions about the existence of a shot from the grassy knoll. According to this report, 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.
Table of Contents
|I. INTRODUCTION AND OVERVIEW||3-7|
|II. DESCRIPTION OF STUDIES BY BRSW AND WA||8-11|
|III. EVALUATION OF THE BRSW AND WA METHODOLOGIES AND CONCLUSIONS||12-17|
|IV. TIMING EVIDENCE FROM MATCHING FEATURES||18-31|
|V. EVALUATION OF THE FBI REPORT||32-32|
|VI. POSSIBLE FURTHER STUDIES||33-33|
|APPENDIX A CRITICISM OF PROBABILITY CALCULATIONS||35-40|
|APPENDIX B ANALYSES OF SOUND SPECTROGRAMS OF "HOLD EVERYTHING..."||41-59|
|APPENDIX C TIMING OF CHANNEL I AND II EVENTS||60-80|
|APPENDIX D POSSIBILITY OF SUPERPOSED RECORDINGS||81-88|
|APPENDIX E SIREN SOUNDS||89-91|
|APPENDIX F POSSIBLE FURTHER STUDIES||92-112|
Tape recording by James C. Bowles, the DPD Communications Supervisor, of the playback of the Dictabelt that recorded Channel 1 from approximately 12:26 to 12:35 Dallas time. This is the channel used for ordinary police duties, on which there was a stuck microphone during the time of the assassination. This recording is 08:13 (8 minutes and 13 seconds) long.
First segment of the tape recording by Bowles of the playback on a Gray Audograph of the Audograph disk that recorded Channel 2 from approximately 12:25 to 12:33. This is the Channel used in the Presidential motorcade by the Dallas Police Chief and the Sheriff of Dallas County. This recording is 05:23 long. There are numerous repeats on this copy.
This is the second segment of the Bowles Channel 2 recording running from approximately 12:33 to 12:37. As discussed in the NRC report, there is a 0.4 second gap between the first and second segments, and the recording speed for the second segment is different [see page 61 of the report]. There are numerous repeats on this copy. This recording is 03:14 long.
FBI recording of original Channel 1 Dictabelt from 12:28 to 12:34, with speed adjusted to make all 60 Hz hums the same. This recording is 07:00 long.
FBI playback from 12:04 to 12:46 of original Channel 2 Audograph disc but with playback on a 33 1/3 rpm phonograph which produced no repeats in the relevant regions. As discussed in the NRC report, the audio output times must be speed corrected. In contrast to Track 7, the 7.5 ips tape was played back at 7.5 ips. This recording is 15:12 long.
This is a copy, made by N. F. Ramsey in 1983, of a copy of the Bowles recording of Channel 1, from 12:23 to 12:38. This recording is 16:21 long.
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