1. Introduction

      I have always believed that President Kennedy’s violent lurch to the rear immediately after being shot in the head constituted the strongest evidence for conspiracy in the assassination. It seemed obvious that the Zapruder film recorded the force of a frontal bullet slamming the President into the seat to his left rear. From the first moment I saw these images in the Zapruder film, I have been impressed by how simple, direct, and powerful they are. Two gunmen firing from perpendicular directions—conspiracy.
      Others have reacted similarly. From many published works, I have selected two for illustrative purposes—an early one and a recent one. In 1967, Sylvia Meagher cited an unpublished manuscript by Thomas Stamm, who had viewed the Zapruder film at the National Archives in 1965 (Sylvia Meagher (1967) Accessories after the fact: The Warren Commission, the authorities, and the Report. Bobbs-Merrill Inc., pp. 33 ff):

    Of greatest importance in the film is the sequence of the fatal shot and its aftermath. This sequence shows President Kennedy thrust violently back against the rear seat, from which he bounces forward and spins off to his left into Mrs. Kennedy’s arms...

    The violent backward thrust of President Kennedy occurs, to the eye, at the instant of impact of the fatal shot. The two events appear to be simultaneous and to have the obvious relationship of cause and effect. The service of truth requires no other explanation.

    That President Kennedy could have been thrust back violently against the rear seat in consequence of a bullet fired from above and behind him seems a manifest impossibility. This sequence in the Zapruder film, occupying a mere fraction of a second, invalidates the official autopsy finding and demolishes the Commission’s thesis and findings of a lone gunman firing from the southeast corner sixth-floor window of the Depository. It makes of the Report a monstrous fabrication erected to obscure the truth which must now be disinterred despite the official verdict.

      Strong words indeed from Mr. Stamm.
      Meagher agreed with him. She then noted:

    Vincent J. Salandria and Gaeton Fonzi conclusively demonstrated the backward recoil by tracing the position of the body in successive frames, using two projectors and projecting one slide upon the other. The resultant diagram (The Greater Philadelphia Magazine, August 1966, p. 44) constitutes conclusive and irrefutable proof that the bullet that sent the President violently backward and to his left was fired in front of and to the right of the car and not from the Book Depository.

      Warming to her subject, Meagher went on to state:

    To the critic who has seen the Zapruder film and gasped at this graphic proof of a conspiracy to kill the President— for there must have been a gunman in front of the car as well as behind it—one thing arouses even more alarm and anguish than the sight of his exploding head: the silence of the Warren Commission (and its lawyers, investigators, and witnesses) in regard to this visible evidence clearly implicating at least two riflemen in the crime.

    That silence, as much as any other single abuse of logic or misrepresentation of evidence in the Warren Report, convicts the Commission of dishonesty and calculated deception. The Commission did not acknowledge the slam of the body against the back of the seat; it did not solicit opinion from experts as to whether that body recoil conceivably could be reconciled with a shot from behind the car; and it did not inform the public—the vast majority of whom will never view the Zapruder film at the National Archives—that the camera had recorded events central to the establishment of the truth and utterly inconsistent with the lone-assassin thesis.

      Meagher concluded her argument by citing a physicist:

    In January 1967 Ramparts published the results of a study conducted for the magazine by Dr. R. A. J. Riddle, assistant professor of physics at UCLA. After studying the relevant segment of the Zapruder film, Dr. Riddle pointed out that the law of conservation of momentum governs the movement of an object hit by a projectile and gives the object a motion in the same direction as the motion of the projectile. After applying that principle to Frames 310–323, Dr. Riddle reached a conclusion that “contradicts the findings of the Warren Commission”—that is, that the shot came from the front and right of the car.

      More recently, David Lifton published a lengthy book recounting his fifteen-year odyssey through Kennedy-assassination material, which led him ultimately to conclude that the President had been killed by a governmental conspiracy which involved, among other things, altering the body en route to Bethesda and falsifying the subsequent autopsy photographs (David S. Lifton, 1980, 1988, Best Evidence: Disguise and deception in the assassination of John F. Kennedy. Carroll & Graf, New York, 755 pp). In the book, he deals with the backward lurch at great length, and tells how important it was to him. Being an engineering major at UCLA, he was prepared to understand the physics of the lurch:

    In March 1965 [Raymond] Marcus told me that the Zapruder frames showed that President Kennedy’s head moved rapidly toward the rear following the fatal shot. I had been a physics major. I appreciated the inviolability of Newton’s laws. What I was shown seemed no mere “hypothesis,” but absolute proof that Kennedy had been shot from the front (Lifton, p. 6).

      In fact, the backward lurch of Kennedy’s body (which Lifton calls the “head snap”) was the piece of evidence that convinced Lifton of the reality of conspiracy in the assassination:

    The head-snap issue was also a turning point for me psychologically. Previously, I could play with the idea of conspiracy as an interesting hypothesis, nothing more; now I had to confront it as a certainty. (Lifton, p. 7)

      Taking Meagher, Stamm, Riddle, and Lifton together, we find a collection of extremely strong statements about how the lurch proves a conspiracy beyond any doubt. In the name of physics, phrases like “manifest impossibility” that the bullet came from the rear, “invalidates the official autopsy finding,” “demolishes the Commission’s thesis of a lone gunman,” “makes of the [Warren] Report a monstrous fabrication,” “conclusive and irrefutable proof” that the bullet came from the right front, “graphic proof of a conspiracy,” “visible evidence clearly implicating at least two riflemen,” “convicts the Commission of dishonesty and calculated deception,” “the camera had recorded events utterly inconsistent with the lone-assassin hypothesis,” “absolute proof that Kennedy had been shot from the front,” and “I had to confront [conspiracy] as a certainty” leave no doubt as to the opinion of these writers on conspiracy.
      These writers were all wrong. To a person, they seriously misunderstood the basic physics of the head shot and ignored the relevant ballistics. This monograph demonstrates that a single bullet from the rear explains all Kennedy’s motions, and that those motions are incompatible with additional bullets from any other directions. All the physics and ballistics needed to reach this conclusion were known and understood at the time of the assassination; no new information was required. They are both simple enough that anyone can do what I have done. You don’t have to be a physics major or a ballistics expert—I am neither. Why didn’t Meagher, Stamm, Riddle, and Lifton get it right? Because they rushed to judgment. They failed to exercise the care and caution that researchers learn early in their education. Why were they so careless? Because they couldn’t imagine that they might be wrong. Because they already knew what the answer was. Because their thought were controlled by factors other than logic. Unfortunately, those factors led them astray, as similar preconceptions have led so many others astray in the Kennedy assassination.
      What about other types of evidence for conspiracy? Compared to a frontal shot, the other evidence pales. For example, consider the single-bullet theory. Proponents of conspiracy contend that because the single-bullet theory can’t be supported, there must have been a conspiracy. To me, their objections to the single-bullet theory have always been much weaker and more indirect as evidence than the lurch was. One reason is that proving a negative assertion (that one gunman could not possibly have fired both body shots to Kennedy and Connally in the allotted time) is so difficult, if not impossible, in practice that it can never become the sole basis for a conclusion. Here, for example, the impossibility is based on the hits to the two bodies coming in less than the 2.3 seconds required for a shooter to reload, aim, and refire with sufficient accuracy. The weaknesses in this reasoning are painfully obvious: suppose the shooter just got lucky with his second shot, or suppose he didn’t aim through the telescopic sight? In either case, he could have fired the second shot in well under 2.3 seconds. Unless some great law of nature is involved, one can’t say that something is impossible.
      Lost in all the fighting over the single-bullet theory is the fact that the traditional time when Kennedy was first hit is an extremely indirect conclusion. Many researchers claim that he was hit while behind the street sign, because when the Presidential limousine emerged at frame 225, he was clutching at his throat. But we don’t know for sure that he was hit or even that he was clutching his throat. Raising both his arms may just have been a protective gesture, in response to the sound of rifle fire. His fists were balled up in front of his face rather than actually grabbing at his throat. Thus from the Zapruder film alone, it is impossible to tell whether the President was really hit by Frame 225. Recall that Mrs. Connally, the only passenger in the limousine who got a good look at the President at that moment, stated specifically that there was no blood on his throat or clothes. We can’t say that he was hit by Frame 225.
      The other major line of evidence for conspiracy is the recollections of the Dallas doctors and nurses of a gaping exit wound in the right rear of Kennedy’s head, which is proposed as proof that he had been shot from the front. The strength of this evidence is the near-unanimity of the Dallas medical personnel on this point. But this evidence has several weaknesses that are seldom discussed. First, the evidence is pure recollection; there are no photographs from Parkland’s Emergency Room that could verify the memories. In other words, the Dallas evidence is anecdotal. Second, the Dallas medical evidence is interpretive: the gaping rear wound is interpreted to be a wound of exit because that’s the kind of hole made by exiting bullets. But it could just as well have been an explosive wound, which can be anywhere. Third, the Dallas recollections contradict the official autopsy photographs, which clearly show a small wound of entrance in the rear of Kennedy’s head and a larger wound of exit just above his right ear and a bit in front of it (not to be confused with the much larger explosive wound at the top of the head). Fourth, the Dallas recollections contradict the Zapruder film, which shows the rear of Kennedy’s head intact and a gaping exit wound over his right ear, just where the autopsy photographs show it. With these two independent sets of photographs agreeing that the exit and explosive wounds are in very different parts of the head from where the Dallas doctors claim to recall it, no one may legitimately choose for the doctors over the photographs. The anecdotal medical evidence from Dallas must be discounted.
      Other minor pieces of evidence for conspiracy are weaker still. A few witnesses reported hearing more than three shots, although about 90% heard three shots (Josiah Thompson (1967) Six seconds in Dallas: A micro-study of the Kennedy assassination proving that three gunmen murdered the President. Bernard Geis Associates, p. 25). But since some witnesses heard up to six shots, and some heard two shots or fewer, this body of evidence must be considered inconclusive.
      Analysis of a highly processed Dictabelt tape from the Dallas Police Department was reported to show a >95% probability of four shots, with the third coming from the grassy knoll area but missing Kennedy (HSCA report). If validated, this would prove a conspiracy just as solidly as a frontal head shot would. This evidence has been overturned by several factors, however, chief among which was that its sounds of a bell and a motorcycle were incompatible with events at the site of the assassination (NRC Ballistic Acoustics report). Lost in the shuffle here also was the fact that this computer analysis was extremely weak and indirect because it was based on highly processed low-grade audiotapes. To the ear, the “shots” were nothing more than a series of clicks and pops, more like static than anything else. Computer analysis like this may never stand on its own—it must be verified before it can be accepted, and no verification was ever available. Thus, the inherent strength of the Dictabelt evidence was greatly exaggerated from the beginning.
      Then there were the witnesses who heard shots from the grassy knoll. This kind of evidence is also very weak, because the witnesses really reported sounds from the direction of the knoll, not necessarily from the knoll itself. Dealey Plaza is such a echo chamber that the sounds may have echoed from somewhere else. Buildings and other structures surround the eastern end of the plaza, and create a complex pattern of echoes. In particular, the semicircular concrete pergola right next to the knoll acts like a lens and reflects sounds from various directions and makes them appear to have originated at the knoll. In Dealey Plaza, let the listener beware!
      Last is the just-plain-silly evidence for a conspiracy which is cited all too frequently by otherwise-serious people. Cigarette butts and footprints in the mud behind the picket fence on the knoll come to mind. Does anyone really think that butts and prints behind the fence had to have been left there by someone firing a rifle at the President? Could no other class of citizen have been responsible? In the same category are the purported puff of smoke and the sightings of men carrying rifles. Without physical validation, this kind of evidence means nothing.
      Thus for all practical purposes, objective evidence for conspiracy in the Kennedy assassination is limited to the backward lurch. Consequently, it is a shame that the lurch has never been fully analyzed. I find it incredible that in spite of nearly forty years of “research” into the assassination, the strongest potential evidence for conspiracy was never investigated thoroughly. Sometimes it seems to me that the assassination community would rather talk than act!
      What’s worse, many of the attempts to deal with the lurch have been of poor quality, marked by bad physics, bad reasoning, or both. (Specific examples are given later.) For now, suffice it to say that the major error of critics was not beginning with the ballistic knowledge of how bullets interact with bodies. By ignoring these well-known principles of ballistics, assassination researchers deprived themselves of the conceptual framework for understanding what they saw in the Zapruder film. Without this constraint, they were free to arrive at ad hoc explanations for the movements they saw, and to make all sorts of errors without realizing it. That is exactly what happened.
      It is very easy to make this kind of error. I did it too, and include myself in those whom I now criticize. For the first year and a half that I studied the Kennedy assassination, I analyzed the Zapruder film without a proper background. Although I got much of it right, I missed the single most-significant fact because I didn’t know the relevant ballistics.
      Dr. Robert Artwohl put me on the right track. In his article in JAMA (Robert R. Artwohl, MD (1993) “JFK’s Assassination: Conspiracy, forensic science, and common sense” JAMA 269 (12), 1540–1543), he succinctly summarized the classical ballistic knowledge about how a bullet actually passes through a body, and cited a contemporary reference book where further details could be found (Vincent J.M. DiMaio (1985) Gunshot wounds: Practical aspects of firearms, ballistics, and forensic techniques. CRC Press, Boca Raton, 331 pp.). When combined with the basic physics of colliding bodies, the material in these two references allows anyone to fully interpret the President’s motions, and proves that he was hit in the head by only a single bullet fired from behind. The next two sections summarize the relevant ballistics, their implications for physics, and the President’s motions as derived from the Zapruder film. The sections after that show that the single bullet created all the observed motions.

Ahead to Movements in the Z-film
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