It would have been absolute insanity by Cuba…. It would have been a provocation. Needless to say, it would have been to run the risk that our country would have been destroyed by the United States. Nobody who’s not insane could have thought about [killing Kennedy in retaliation].Another theory says that Cuban exiles, tired of waiting on Kennedy to install them in Cuba decided, or were directed by elements of the CIA to kill Kennedy.Seeing Cuba as the greatest threat in the Cold War, CIA brass wanted Kennedy to be more proactive in dealing with Castro.The KGB/Soviet theory(Topham/Topham Picturepoint/Press Association Images)Given that Kennedy had stared down the Soviet Union over Cuba and the assassination happened in the middle of the Cold War, this theory is plausible, to a point.Throughout the Cuban Missile Crisis, Kennedy showed no appetite for war. Johnson subsequently escalated US involvement in Vietnam and, if not more war hungry himself, he certainly had more hawkish advisers. So the Soviet end game is hard to see.The theory goes that the Soviet government was embarrassed by Cuba and had Kennedy killed. Soviet defector Ion Pacepa claims to have had a conversation with Romanian leader Nicolae Ceausecu about ten international leaders the KGB either killed or tried to killed.Another theory says that Kennedy was a communist puppet who had “turned American” and was dragging his heels on delivering communism to the States.The Warren Commission found no evidence of Soviet involvement, but it has been claimed Johnson ordered the commission not to bother looking into the Soviets, less the world be plunged into war for the third time in 50 years.The fact that Oswald spent two years in Russia and had a Russian wife also lends weight to this theory. The Mafia theory FBIAmerica in the 60s had Mafia bosses. Lots of them. And they were powerful both at home and abroad.Their network, their proficiency with killing people and the fact that Oswald assassin Jack Ruby was a known Mafia acquaintance give this theory some legs.That’s means and circumstance but what about motive? Castro had shut down lucrative casinos in Cuba, so his removal would have helped, but was that enough to kill a president?Kennedy’s brother Bobby, who was the Attorney General, had vowed to clamp down on organised crime. Certainly, Bobby had angered the Teamsters’ Union boss Jimmy Hoffa by attempting to prosecute him for racketeering.But again, is that motive to kill his brother?The CIA had contact with mob bosses about an attempt on Castro, did they then feel double-crossed by the Kennedy Administration?Another theory is that Kennedy and mob boss Sam Giancana shared a mistress making this a straight-up crime of passion. The New Orleans theory (Wikimedia Commons)The reason most people have for disbelief in the Warren Commission findings is that everything is too neat with a story that one man did it and another shot him in revenge.The report contains glaring inaccuracies and inconsistencies which have been chased over time. Even the House Select Committee on Assassinations found a “high probability” that at least two people fired at the President.Louisiana District Attorney Jim Garrison was the only man ever to bring someone to trial in connection with the assassination, but even that didn’t lead to a conviction as Clay Shaw was cleared by a jury just an hour into deliberations.The theory goes that Shaw, Oswald and David Ferrie, with or without the aid of the mafia or Cuban exiles, plotted to assassinate Kennedy because they didn’t like his politics on a number of issues.The reason it is in any plausible is that it involves the fewest number of people. The other theories involve a myriad of conspirators and no group that size has been known to hold a secret that long.It falls down on any real evidence, however.It is known that Oswald spent time in Louisiana in the months leading up to the shooting, that David Ferrie lied about knowing Oswald earlier than 1962 (the picture above shows Ferrie and Oswald together in 1955) and that Clay Shaw had at the very least been considered as a CIA operative.But does any of that point to the most high-profile assassination of all time?Jim Garrison thought so and his book “On The Trail Of The Assassins” lays out this theory.The RestOther theories involve a shadowy cabal of bankers, UFO cover-ups, the Israeli government, the Illuminati and even George HW Bush.Read: Parnell and JFK: Parallels Up For DiscussionIn photos: JFK visits Ireland in 1963 NEXT FRIDAY WILL mark 50 years since the assassination of then-US President John F Kennedy.Nobody was ever convicted of the assassination due to the murder the following day of Lee Harvey Oswald by Jack Ruby. The findings the following year by the Warren Commission that both Oswald and Ruby acted alone have been debate, disputed and supported in equal measure over the half century that has passed.Much of the reading and viewing on the subject is tied to a lot of circumstance and conjecture, but the theories abound.Here are just a few.The Lyndon B Johnson theory(Henry Griffin/AP Photo)As far as motive goes, the Vice-President certainly stands out. With Kennedy gone, Johnson became the 36th President of the United States, the most powerful man in the world.That Kennedy and Johnson contested the Democratic nomination in 1960 and the assassination occurred in Johnson’s home state both lend weight to suggestions that he may have been involved. As does the well-known antipathy between Kennedy’s inner circle and Johnson (Bobby Kennedy referred to LBJ in his eulogy to his brother as a “garish sun”).A new book by an advisor to Richard Nixon, Roger Stone, claims Nixon believed LBJ was involved.The theory is that rich tycoons who stood to benefit from LBJ’s more pro-market stance paid for the assassination.As-yet-unreleased recordings are said to contain evidence that Jackie Kennedy also believed that Johnson was involved. Johnson is said to have believed the next theory.The Cuban Government theory(AP Photo)“Kennedy was trying to get Castro, but Castro got him first,” said Johnson in a 1968 interview.Given that the US had attempted to assassinate the Cuban leader a number of times, it is understandable that Castro would be a little upset and want a measure of revenge.The US attempt to overthrow him that led to the Bay of Pigs fiasco and the Cuban Missile Crisis would have backed Castro into a corner. The theory goes that to counteract this, he had the Mafia kill Kennedy.In 1977, Castro dispelled the idea.