Earl Warren did it, Lyndon Johnson assisted, and the American media played along. Oh sorry, you meant the murder not the coverup.
Seriously though, and without trying to sound too much like a paranoid conspiracy theorist, a plausible case can be made that a coup d'etat, or an semi-apprehended coup d'etat happenend on November 22, 1963. Not that Johnson was a conspirator, but he may well have been an unwitting benefactor.
