There are many ties between the CIA and the Mafia, and the cuban exiles. There was the Cia/Mafia plots to kill Casrto, and there were the Mafia's involvement in Cuba before the revolution, and involvement with the anit-Castro movement in the South.

You have these groups working together with money/guns/ and eventually a hatred of JFK. Also Oswald had ties to the New Orleans mob through and uncle he lived with in his youth.

Does this mean they killed JFK?

I don't know, but there was motive, and means so anything is possible.