Fifty-nine Witnesses: Delay on Elm Street By Vince Palamara
UPI's Four Days (1964), p. 17--- In the right hand picture [a frame from the Muchmore film], the driver slams on his brakes and the police escort pulls up.
Case Closed by Gerald Posner (1993),p. 234---"Incredibly, Greer, sensing that something was wrong in the back of the car, slowed the vehicle to almost a standstill." AND - Gerald Posner, with Dan Rather, on CBS' "Who Killed JFK: The Final Chapter?", 11/19/93---By turning around the second time and looking at JFK as the car slows down, Posner says that "What he [Greer] has done is inadvertently given Oswald the easiest of the three shots."
ABC Reporter Bob Clark(rode in the National Press Pool Car)---Reported on the air that the limousine stopped on Elm Street during the shooting [WFAA/ ABC, 11/22/63];
DPD James Chaney (one of the four Presidential motorcyclists)---stated that the Presidential limousine stopped momentarily after the first shot (according to the testimony of Mark Lane; corroborated by the testimony of fellow DPD motorcycle officer Marion Baker: Chaney told him that "...at the time, after the shooting, from the time the first shot rang out, the car stopped completely, pulled to the left and stopped...Now I have heard several of them say that, Mr. Truly was standing out there, he said it stopped. Several officers said it stopped completely." [2 H 44-45 (Lane)---referring to Chaney's statement as reported in the Houston Chronicle dated 11/24/63; 3 H 266 (Baker)];
I've only listed a few . You can go to mcadams.posc.mu.edu/59wit.htm