One of the many ludicrous claims made by Alteration Fantasists [Altfans] is that the Presidential limo came to a complete stop around the time of the head shot and, because the Z-film doesn't show this limo stop, it must be concluded that the film was altered. Most go a little bit further, insisting the Z-film doesn't even show the limo slowing down, let alone coming to a stop:
"...the fact that in the film (contrary to eyewitness testimony) JFK’s limousine does not stop or reduce speed during the assassination. At the time of the assassination, in the Zapruder film, JFK’s limousine glides forward at a steady (and unusually low) speed of about 11 mph; the car definitely does not stop or slow down."
["Grassy Knoll Shots? Limousine Slowdown?", Donald E. Wilkes Jr]
It is difficult to know what word to use to describe this claim - "Mistaken" would be kind, "Fraudulent" seems a bit harsh. Whatever the case, it's completely wrong and Wilkes Jr goes on to build his case on the back of this error. In mitigation it must be conceded that the radical deceleration of the limo shown in the Z-film isn't readily apparent. This is due to the background having few visual cues at the moment of the head shot. In the version of the Z-film below, Ant Davison has created a new way of looking at the Z-film by keeping all the visual information in place to create a backdrop against which we can clearly see the movement of the limo relative to it's surroundings.
In this version it is absolutely clear that just before the head shot the limo radically decelerates to almost walking pace:
This deceleration of the limo is an obvious fact. It is shown in the Z-film, the Nix film, the Muchmore film and the Bronson film. It is the reason the distance between the limo and the follow-up car rapidly diminishes, it is the reason the outriders suddenly catch up with the limo, it is the reason Hill can make the gap.
The likes of Wilkes and his Altfan buddies claiming the Z-film doesn't show this deceleration is a case of incredibly poor research and the arguments for alteration built on this non-observation are totally bogus.
Some of the outriders are said to have reported that the limo came to a complete stop for a brief second. The fact is that it was the outriders themselves who came to a complete stop as they suddenly caught up with the decelerating limo. This may have added to the impression that the whole motorcade had come to a brief halt and having JFK's head explode a matter of feet away may have also been distracting.
For those Altfans who believe the Z-film was altered to remove a complete limo stop, however brief, there are two seeming impossibilities:
1) The Nix, Muchmore and Bronson films must be similarly altered.
2) In all these films we see Jackie and the occupants of the limo constantly moving, Hill racing toward the limo, the outriders, the follow-up vehicle and the people stood on Elm Street watching the motorcade all moving at all times. For a limo stop to be removed all of these people must "freeze" for the amount of time removed to delete a limo stop. Everyone must stop moving at exactly the same moment and resume movement at exactly the same moment. In their childish beliefs, Altfans convince themselves it's just a matter of dealing with the movement of the limo. Everything else can be overlooked!
The limo slowed to almost walking pace. It didn't stop. And the Z-film most ceratinly wasn't altered in order to hide something that never even happened.