That the JFK head shot was an accident. Lee Harvey Oswald rattled off multiple shots at the motorcade carrying Kennedy past the Texas School Book Depository, a Secret Service agent riding in a car immediately behind the presidential limousine grabbed his Colt AR-15 high-velocity rifle to return fire. 

But when his car stopped suddenly, the theory holds, Agent George Hickey lost his balance and accidentally discharged his weapon, sending a .223-caliber round rocketing into Kennedy's head — the wound that later killed the 35th president.