Different theories on who shot Kennedy and alteration of the Zapruder film
... The “Muchmore” film shows the limousines brake lights on for nine frames (about half a second) during frames 311-319 of the Zapruder film. ... The slowdown is not noticeable in the film, it represents a deceleration of about 0. ... Alvarezs data is accurate, the sudden reduction in speed that he found would seem to give further evidence of alteration in the Zapruder film. ... In the film, at least four witnesses saw blood and brain from Kennedys skull blow out toward the rear of the limousine. When I watched the film, the main spray went forward, but the mist was blown backwards, because they were moving.