The Struggle for the Revolver
Officer McDonald testified that during his struggle with Oswald over the revolver he heard the hammer snap and felt a primer dent on misfire, but no such firing pin impression was found on any cartridge in the revolver. Technical analysis showed that the firing pin cannot strike a cartridge unless the hammer is drawn fully back by a complete trigger pull, making a misfire from such a trigger pull unlikely. Although a finger could theoretically be interposed between hammer and cartridge, the strong hammer spring would make the impact clearly felt. Because the cylinder and trigger are interconnected, Oswald could not have fully pulled the trigger if McDonald was firmly grasping the cylinder, and a sudden grab of the gun would have produced an audible trigger snap rather than a misfire.
The Paraffin Test
The Dallas police performed a paraffin test on Oswald’s hands and right cheek during interrogation; the hands reacted positively while the cheek did not. The test applies warm liquid paraffin to pick up surface residues, which are then tested with diphenylamine or diphenylbenzidine for nitrates, theoretically indicating recent firing of a weapon. The chapter explains at length that the test is completely unreliable: a positive reaction can be triggered by tobacco, Clorox, urine, cosmetics, matches, fertilizers, soil, or even mere weapon handling, while a person who has fired a rifle may show no reaction because a rifle’s sealed chamber prevents nitrate-bearing gases from escaping back toward the shooter. FBI experiments demonstrated both kinds of unreliability, including an agent who fired three rounds of Mannlicher-Carcano ammunition and tested negative on both hands and cheek. Oak Ridge neutron-activation analysis of Oswald’s paraffin casts found barium and antimony, but these elements were present in both rifle and revolver ammunition, were also found on the outside surface of the cheek cast (which had not touched Oswald), and could be traced to many common items, so their presence could not be linked to rifle firing.
The Walker Bullet
On April 10, 1963, a severely mutilated bullet weighing 148.25 grains was recovered from General Walker’s home after an attempt on his life. The bullet displayed the rifling characteristics of the C2766 rifle and otherwise matched the Western 6.5-millimeter Mannlicher-Carcano bullet, but Frazier concluded that the mutilation prevented a determination of whether it had been fired from that rifle. Nicol agreed that positive identification was impossible but concluded there was “a fair probability” the bullet came from the same rifle as the test bullets.
FINGERPRINTS AND PALMPRINTS
Two fingerprint and palmprint experts testified: Sebastian Latona, supervisor of the FBI’s Latent Fingerprint Section with over 32 years of experience, and Arthur Mandella, a New York City police detective and fingerprint instructor with 19 years in the field. Both had extensive examination and courtroom experience, and their conclusions were identical except as noted in the chapter.
General Principles
Fingerprints and palmprints are produced by permanent ridges that appear 2–3 months before birth and remain unchanged until death; a clear impression contains 85 to 125 identifiable points, and no two prints share the same points in the same relationships. Law-enforcement “inked prints” are carefully taken, while prints accidentally left at crime scenes are “latent prints,” and identification requires finding no inconsistencies between latent and inked prints and sufficient similarity in points and their relative positions. While some foreign agencies require a minimum of 16 matching points, U.S. experts evaluate each print on its own merits with no fixed minimum. Palmprints are equally distinctive but are recorded less often because they are harder to classify, though they are common on heavy objects. Latent prints arise from perspiration (water, fatty or protein material, and salt) and can be developed by lighting, powder, or lifting with adhesive; absorbent surfaces like paper, unfinished wood, or unfinished metal usually require iodine fumes or silver nitrate solution to develop prints. Not every contact leaves a latent print, since smooth nonabsorbent surfaces, lack of perspiration, or evaporation can prevent a print from forming.
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