“Back and to the Left”: The Zapruder Film
The most striking moment of the Zapruder film arrives at frame 313 when President Kennedy's head explodes and his entire upper body is slammed violently backwards and leftwards. Although I don't believe it's accurate to say, as Reitzes does, that the “head snap” has been held up by critics as “irrefutable proof of conspiracy”, there is no doubt that to the majority of us laymen it certainly gives the immediate impression that the fatal shot came from the right front. In fact, after Zapruder's home movie was shown on television for the first time in 1975, public outrage was so great that it ultimately resulted in the formation of the House Select Committee on Assassinations.
But as Reitzes is quick to point out, numerous medical experts convened by government panels have consistently reassured the American public that “back and to the left” doesn't prove anything. He quotes experts for the Rockefeller Commission in 1975 who were “unanimous in finding that the violent backward and leftward motion of the President's upper body following the head shot was not caused by the impact of a bullet coming from the right front.” One of these specialists, Dr. Alfred Olivier—who had previously worked as the chief ballistics expert for the Warren Commission—claimed, unsurprisingly, that the President's movement “could not possibly” be the result of a frontal shot and “attributed the popular misconception to the dramatic effects employed in” movies and television.
However, the government's experts failed to provide evidence to support their assertions. Even in the 1970s, films showing victims of rifle shots to the head were readily available. I myself have seen old black and white wartime films of kneeling prisoners being shot in the back of the head with bolt action rifles. In each case, the victims did not lurch drastically back towards the shooter but fell forwards onto their faces. Regardless, the Rockefeller experts chose not to provide documented examples to buttress their position and instead offered two theories, the “neuromuscular reaction” and the “jet effect”, neither of which has withstood scrutiny.
The “jet effect” suggests, that in a similar fashion to the thrust developed in a rocket or jet engine in response to its exhaust, the explosive exiting of blood and brain matter from the right side of Kennedy's head created a corresponding propulsive momentum in the opposite direction. The theory was the brainchild of Nobel Prize-winning physicist and stern Warren Commission supporter, Dr. Luis Alvarez, who—though he kept the fact to himself—was paid by the government to conduct his study. (David Wrone, The Zapruder Film: Reframing JFK's Assassination, p. 103) Alvarez demonstrated the effect by shooting a high powered rifle at melons resting on fence posts which caused the melons to recoil back towards the shooter. But as scientist Dr. Donald Thomas explained in his fine book, Hear No Evil: Social Constructivism & the Forensic Evidence in the Kennedy Assassination, Alverez had rigged the tests.
Firstly, the melon is not, as Dr. Alvarez claimed, a “reasonable facsimile of a human head.” In fact, as Dr. Thomas writes, “a melon differs from a human head in precisely those characteristics that make the jet effect implausible in the latter, but possible in the former.” (Thomas, p. 359) A melon weighs approximately half as much as a human head and so requires less energy to set in motion. It also lacks a bone which means that it offers little resistance to a bullet so that there is little deposition of momentum and, consequently, very little force to overcome. “By minimizing the deposition of momentum, using a target with little resistance,” Dr. Thomas writes, “Alvarez was free to work on the other end of the equation, by jacking up the velocity.” Dr. Alvarez used a high-powered 30.06 rifle instead of the lower velocity Mannlicher Carcano and hot-loaded his cartridges to 3000 feet per second. (Ibid) When another Warren Commission defender, Dr. John Lattimer, attempted to duplicate Alvarez's tests using an actual Mannlicher Carcano and factory ammunition, he did not achieve the jet effect. His melons simply fell off the pedestal; sometimes backwards and sometimes forwards. (Ibid, p. 362)
Dr. Thomas also makes the point that in order for the jet effect to be a viable explanation for the backward motion, the exit wound, or the “vent”, would have to have been in the very front of the skull. But the massive wound to Kennedy's skull involved most of the right side, from the temple back to the occiput. And if the vent was on the right side, “then the jet effect would have driven the head to the left (the side opposite the vent) not backwards.” (Ibid, p. 358) As Dr. Thomas summarizes, “...the President did not have an exit wound in a position that would have caused his head to move rearward if there was a jet effect.” (Ibid, p. 370)
As it's explanation for the backwards motion, the HSCA favoured the neuromuscular reaction—a theory that was put to the committee by ballistics expert, Larry Sturdivan, who had worked at Edgewood Arsenal under Dr. Alfred Oliver. Sturdivan put his hypothesis in the simplest possible terms for last year's Cold Case: JFK television special:
“The tissue inside the skull was being moved around. It caused a massive amount of nerve stimulation to go down his spine. Every nerve in his body was stimulated. Now, since the back muscles are stronger than the abdominal muscles, that meant that Kennedy arched dramatically backwards."
But as Dr. Thomas explains, "Sturdivan's postulate suffers from a patently anomalous notion of the anatomy. In any normal person the antagonistic muscles of the limbs are balanced, and regardless of the relative size of the muscles, the musculature is arranged to move the limbs upward, outward, and forward. Backward extension of the limbs is unnatural and awkward; certainly not reflexive. Likewise, the largest muscle in the back, the 'erector spinae', functions exactly as its name implies, keeping the spinal column straight and upright. Neither the erector spinae, or any other muscles in the back are capable of causing a backward lunge of the body by their contraction." (Thomas, p. 341) Additionally, the type of reaction Sturdivan posits is simply not in keeping with what we see on the Zapruder film. Kennedy's movement did not begin with an arching of the back. As the ITEK corporation noted following extensive slow motion study of the Zapruder film, his head snapped backwards first, “then his whole body followed the backward movement.” (ITEK report, p. 64)
Reitzes writes that immediately before the backward motion appears on the Zapruder film, Kennedy's head moves forward by 2.3 inches. This, he suggests, is the “instant of impact” of a bullet entering the back of the head. This alleged forward motion was first reported by Josiah Thompson in his book, Six Seconds in Dallas, but Thompson has since changed his mind about its very existence. In his online article, Bedrock Evidence in the Kennedy Assassination, Thompson writes: “In the years since those measurements were made, I've learned I was wrong. Z312 is a clear frame while Z313 is smeared along a horizontal axis by the movement of Zapruder's camera. The white streak of curb against which Kennedy's head was measured is also smeared horizontally and this gives rise to an illusory movement of the head. Art Snyder of the Stanford Linear Accelerator staff persuaded me several years ago that I had measured not the movement of Kennedy's head but the smear in frame 313. The two-inch forward movement was just not there.”
On the other hand court certified Crime Scene Investigator, Sherry Fiester, believes Thompson's initial observations were correct. She characterizes the alleged forward motion as a "movement into the force" of a shot from the front. Citing a number of ballistics studies, Fiester explains, "Once a bullet enters the skull...the bullet immediately loses velocity. The loss of velocity results in a transfer of kinetic energy...This initial transfer of energy causes the target to swell or move minutely into the force and against the line of fire." (Fiester, Enemy of the Truth: Myths, Forensics, and the Kennedy Assassination, p. 245)
The reader will have to do their own research and decide for themselves whether Thompson or Fiester is correct but there is something else that needs to be considered. That is, the motions of the other occupants of the Presidential limousine who, the Zapruder film shows, all moved forward at the time of the head shot and continued their forward motion after Kennedy's body was sent hurtling backwards. This is clearly demonstrated in the these two animations from researcher David Wimp:
It stands to reason that these people, who all made the same motion, were all affected by the same force. That force would appear to have been the deceleration of the limousine. If Dr. Alvarez's calculations are correct, then it appears that the President's car began to slow down a little under one second before the head shot at approximately Zapruder frame 300. (Thomas, p. 340) This was apparently the result of Secret Service driver Willaim Greer touching the brakes—an inexplicable act that caused many bystanders to believe that the limousine came to a virtual standstill during the assassination.
So, if Greer tapping the brake caused the other limo passengers to lurch forward, then it quite probably was responsible for any forward motion on the President's part. There is, then, no compelling reason to accept Reitzes' hypothesis that Zapruder frames 312 to 313 captured the “instant of impact” of a shot from the rear.