A combat-hardened ex-Marine and police sharpshooter Craig Roberts, author of "Kill Zone: A Sniper Looks at Dealey Plaza", asked,
"How in the world could anyone look at that {Zapruder} film and say that the fatal head strike had come from the rear? The so-called experts who stated that the rearward jerk of Kennedy's head was due to 'muscle reaction,' 'jet force from an erupting bullet' or some other violation of the laws of physics, had obviously never served in combat, where witnessing high-velocity bullet strikes was commonplace...
"Some of the supporters of the Warren Commission...stated that the bullet came from the rear because the eruption of brain matter and blood came out of the front of the president's skull. I saw something else. In a head shot, the exit wound, due to the buildup of hydrostatic pressure, explodes in a conical formation in the down-range direction of the bullet. Yet in the Zapruder film, I could plainly see that the eruption was not a conical shape to the front of the limo, but instead was an explosion that cast fragments both up and down in a vertical plane, and side to side in a horizontal plane. There was only one explanation for this: an exploding or 'frangible' bullet. Such a round explodes on impact--in exactly the manner depicted in the film."