The idea that evolved into the single bullet theory originated with Dr. Humes in his Warren Commission testimony. This is spelled out in “Passion for Truth” by Arlen Spector, pate 80. Here is a snip from that page:
Our Friday interview with Humes and Boswell produced a revelation: The bullet that passed through Kennedy’s neck proceeded in a straight line, struck nothing solid, and exited with great velocity. The doctors had not mentioned this in their autopsy report. “The missle struck no bony structures in traversing the body of the late president.” Humes testified when I questioned him the following Monday. “Therefore, I believe it was moving at its exit from the president’s body at only very slightly less than that velocity, so it was still traveling at great speed.”
Humes then referred to Commission Exhibit 398, a frame of the Zapruder film that showed Kennedy raising his hands to his neck, presumably after being shot there. “I believe in looking at Exhibit 398, which purports to be at approximately the time the president was struck,” Humes said, “I see that Governor Connally is sitting directly in front of the late president, and suggest the possibility that this missile, having traversed the low neck of the late president, in fact traversed the chest of Governor Connally.”
The origin of the idea/opinion that evolved into a hypothesis, then theory and conclusion began with Dr. Humes. It has been extensively tested and evaluated by the scientific community time and time again over the past sixty-plus years and it is strongly supported by the vast majority of the scientists who have tested it. The Knott Labs study tries in vain to disprove the single bullet conclusion but fails miserably. No truly unbiased jury (they are all supposed to be unbiased) could ever believe that the Knott Labs study disproves the single bullet conclusion.