I haven't read as many books on the assassination as Plaw, but I went on a JFK binge after seeing the movie and read approximately 15 different books. No one theory is without its flaws. I personally don't think Cuba was involved with Oswald. If they were, the US and the American people would have definitely supported attacking Cuba, where just one year before JFK's murder Cuba was holding nuclear weapons for the Soviets.

If it was the Mob, they farmed their work out by hiring non-mafia gunmen. Not out of the realm, to be sure, but not all that likely. There were lots of mob connections to JFK, Ruby, and Oswald, but I think they were not involved in the killing.

Again, this has just as many flaws as the other versions. But I think the CIA/FBI was in on it. Not to the level Oliver Stone portrays in his film, but a few key people. Why? JFK was working to dissolve the CIA and some very prominent people lost their jobs under JFK (Allen Dulles, Helms, etc.) Other reasons: JFK and the CIA were at odds the entire tenure of his administration. He blamed them for the faulty info with the Bay of Pigs fiasco. They pressured to get Kennedy to invade Cuba and then commit more troops to Vietnam. And Kennedy opposed both and was always skeptical of the CIA after the Bay of Pigs. And Hoover from the FBI hated the Kennedys and most certainly wasn't in on the killing, but was also not sorry to see him go.

Throw in the fact that Oswald was in the CIA, along with some of his buddies like Clay Shaw, David Ferrie, and
Guy Bannister. Oswald was obviously on some kind of covert mission for our government in order to be able to travel so freely to Cuba and Russia after renouncing his US citizenship.

IMO, it's a mystery that no one will ever have the complete answer to, not even 100 years from now.