The John F. Kennedy assassination Dictabelt recording was a Dictabelt recording from a motorcycle police officer's radio microphone stuck in the open position that 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 from 1978, in which the HSCA used it to conclude 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. Verbal time stamps were made periodically by the police radio dispatcher and can be heard on the recording. 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. 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." 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 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