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 (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. 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." Using an amateur film shot of the motorcade, 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 usually 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 came from his motorcycle. He said that the other sounds on the recording did not match any of his movements. 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. 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