Every November 22, people worldwide remember and ponder the assassination in 1963 of President John F. Kennedy. He was sitting in the back seat of a convertible (the top was down) when bullets fired from a rifle tore into him and a fellow passenger.
The assassination was caught on 8mm film by Abraham Zapruder. Digital enhancement of that famous film shows part of Kennedy's skull getting blown off. JFK was barely alive as the convertible sped to the nearest hospital; he died shortly after arriving there. The damage to his brain was so great that even today's medical techniques couldn't have saved JFK.
Conspiracy theories have persisted since the time of the assassination: the Mafia did it, the Teamsters did it, the CIA/FBI/Secret Service did it, Congress did it, the Federal Reserve did it, LBJ (the vice president) did it, the Communists did it, the Cubans who hated Castro did it, and the two guys behind the grassy knoll did it.
Conspiracy theorists do not believe that a lone gunman did it. The lone gunman was Lee Harvey Oswald. Oswald didn't get to say much in his defense except, "I'm a patsy," implying that he knew who really did it. Two days after Oswald shot Kennedy, Jack Ruby put a fatal bullet into Oswald.
The Warren Commission conducted the federal government's official investigation of JFK's assassination. Its 27-volume report said that Oswald, an ex-Marine, acted alone in shooting JFK from a sixth floor window of a book storage building. But to this day, and probably far into the future, many people dispute this "lone gunman" theory. They believe JFK's death was a result of a conspiracy by one or more groups of people who felt threatened or deserted by JFK. The fact that Oswald was murdered while accompanied by a dozen Dallas policemen only strengthens the suspicions of the conspiracy theorists. The Warren report, they say, is merely a government whitewash of the "true" facts.