Who really shot John F. Kennedy?

I was always taught that JFK was shot by Lee Harvey Oswald in a book depository, but then I heard that he was shot in a gry knoll by David Ferrie, and I heard another story where Ricky White said that his father Roscoe White had admitted to shooting JFK in the gry knoll, and that he had ties to Lee Harvey Oswald in the Marines and also his wife knew Jack Ruby. Also there were so many witnesses that rushed over to the gry knoll area after JFK was shot. Another person told me that he was shot by the CIA from a storm drain. Another story I even heard was that he was shot by the limo driver and that is why he was driving very slowly while the shots were being fired and they did not try to protect the body. Who really killed JFK because I am hearing so many conflicting stories?