Perhaps the most controversial JFK assassination theory comes from Howard Donahue, a ballistics and firearms expert. Hired by CBS in 1967 to help test and assess theories about the JFK shooting, Donahue came away with strong misgivings about the Warren Commission's work and began his own research, the findings of which are documented in "Mortal Error: The Shot That Killed JFK" by Bonar Menninger, and reinforced in a second book, "JFK: The Smoking Gun" by Colin McLaren, an Australian police detective. The McLaren book was made into a television documentary of the same name aired by a small cable network, Reelz, on the 50th anniversary of Kennedy's death.

The theory is shockingly radical and non-ideological. Instead of conspiracies revolving around the CIA, the mafia, Fidel Castro, or shadowy military cabals in high places, Donahue claims that Kennedy was killed by a bullet fired accidentally from an AR-15 rifle held by one of his own Secret Service men, riding in a chase car directly behind the Presidential car. That man, George Hickey, was sitting precariously atop the seat back in the left rear passenger seat when Oswald's first shot rang out. Hickey reached down for the AR-15 stored at his feet and was releasing the safety when the second shot came. As he started to look over his right shoulder to identify the source of the shots the driver of the chase car, also alerted by the shots and aware of the President's peril, abruptly changed speed and direction. The car lurched. Hickey accidentally pulled the trigger, discharging his weapon. It was this shot that killed the President.

Hickey (partially obscured), in the Secret Service chase car, with the AR-15, moments after accidentally shooting President Kennedy?

Hickey sued Bonar Menninger over his book, but a court ruled he'd waited too long to do so and "Mortal Error" remained on bookstore shelves, unrevised. Much to the puzzlement of its author, it did not sell well, and has languished in relative obscurity until now. It will be interesting to see if the documentary based on McLaren's book sparks public interest. In addition to McLaren's ballistics calculations, his allegations that Kennedy's Secret Service detail was in poor shape after a late night of drinking and carousing is damning.