Answer:
The conspiracy theory of the FBI regarding the assassination of President John F. Kennedy was that Lee Harvey Oswald acted on his own. Moreover, the death of Oswald two days later at the hands of Jack Ruby was also an independent incident, and that no other else was involved in the whole thing.
Explanation:
The assassination of President John F. Kennedy took place on November 22, 1963, while he was on a top limousine with his wife Jackie Kennedy, Texas Governor John Connally, and his wife. The gunshot had come from a far distance, wounding the governor but critically injuring the President.
The FBI, along with the Warren Commission, believed or proposed the theory that the President was killed by Lee Harvey Oswald and that he acted alone. Moreover, the subsequent killing of Harvey by Jack Ruby was also found to be Ruby's own doing and does not involve anyone else.
But even though these findings were thought to be true, many still continue to question them and sought to come up with their own theories.