Lee Harvey Oswald fired the bullet that killed Kennedy. The physical evidence from the crime scenes, including ballistic matches, palm prints, and fiber analysis, which has been tested and retested by forensic experts for more than five decades, leaves no serious doubt about who fired the fatal shot. So the Warren Commission was right about the identity of the assassin. But that is the easy part of the mystery. The far more difficult question is: Did Oswald act at the behest of others? The Commission left this portal open by saying it could not exclude the possibility that Oswald was part of a conspiracy.

A lone gunman can act for a conspiracy, as in the plot of Frederick Forsyth’s The Day of the Jackal. Consider, for example, the assassination that had probably the most momentous consequences in history, the shooting of Archduke Franz Ferdinand, the Hapsburg heir to the Austro-Hungarian throne, in Sarajevo on June 28, 1914. As in the case of the JFKassassination, one young man, Gavrilo Princip, fired the bullet that killed the Archduke in his open-top Gräf & Stift Double Phaeton limousine. Since the car took a detour, no one could have known in advance that the Archduke would be at that place at that time, and it initially appeared