The CIA were involved, certainly - but there were other forces at work, as well - the Pentagon/US Military was certainly involved.
LBJ was huge Zionist. Kennedy had been preventing the Zionist Entity from becoming a nuclear power. His brother Bobby, as Attorney General was looking into whether the Zionist Lobby, the predecessor organizations to AIPAC, were acting as "unregistered foreign agents". So that is two reasons why the Mossad may have been involved as well. As soon as LBJ had seized power - he replaced RFK as Attorney General, and reversed those fair and wise policies from the JFK Administration.