Report of the President's Commission on the Assassination of President John F. Kennedy

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.