Corsican Mafia did the hit. Most likely under the instructions of either American Mafia or a faction within the government. Odds are none of the big players we'd expect were involved. It was probably a personal matter. JFK had a list of enemies as long as your arm. It comes with the territory of being a pragmatic bad ass.
Oswald was a Triple Agent working for the US for the Russians for the US for the Russians for the US...
HANKERING FOR SOME BEEF CURTAINS