JFK files likely to expose CIA cover-up, say experts

It's the mystery that still baffles the world 55 years on - the assassination of US President John Fitzgerald Kennedy.

For decades, the existence of secret US government files linked to Kennedy's assassination on that sunny day in Dallas has helped fuel conspiracy theories that others besides Lee Harvey Oswald were involved in his murder.

On Friday, the public will finally get a deeper look at the collection with the release of the final batch of 3000 CIA files related to the murder, which shocked the world and is often referred to as the day America lost its innocence.

John F Kennedy motorcade, Dallas, Texas in November 1963. Photo / Getty

Former New York Times correspondent Philip Shenon, the author of A Cruel and Shocking Act, told the ABC's 7.30 the assassination changed America "in so many ways".

"The only other comparison is 9/11 but this is the event that really made Americans believe that they couldn't trust their government and they couldn't expect their government to tell them the truth," Shenon said.

For many, the big question remains: Was anyone other than Lee Harvey Oswald involved in the assassination?

President John F. Kennedy and his wife Jackie after their arrival at the airport for the fateful drive through Dallas in 1963. Photo / Getty

The Warren Commission in 1964 concluded that Oswald had been the lone gunman, and another congressional probe in 1979 found no evidence to support the theory that the CIA had been involved. But other interpretations, some more creative than others, have persisted.

"Immediately after the assassination, the CIA and the FBI wanted desperately to portray Oswald as a lone wolf, a guy they never could've stopped," Shenon said.

"Well, the truth seems to be that actually the CIA and the FBI knew a lot about Oswald and if they just acted on the information in their own files then the assassination would've been prevented, and I think we're going to see a lot more information along those lines."

Surrounded by detectives, Lee Harvey Oswald talks to the media as he is led down a corridor of the Dallas police station. Photo / AP

Lee Harvey Oswald defected to the Soviet Union in 1959, before returning home. At the height of the Cold War and just weeks before the assassination, Oswald travelled to Mexico City, visiting both the Soviet Embassy and the Cuban Consulate, and it beggars belief that a known defector meeting then enemies of the homeland was not a keen interest to the local CIA chief.

"In particular, the story that the CIA told the Warren Commission is that they did not know much about this man who passed through. That is another story that is basically false. They were paying very close attention. Six weeks before the assassination. And I think we'll find out more of the nature of that."

It will take days and weeks to make sense of the documents.

"You know the conspiracy theories you hear about the Mafia or space aliens or whatever - for most of them there's absolutely no evidence to support them," Shenon said.

"There is evidence to support the idea though that other people knew what Oswald was going to do and may have encouraged him to do what he was going to do and by definition that is a conspiracy."

This image provided by the Warren Commission, shows Warren Commission Exhibit No. 697, President John F. Kennedy at the extreme right on rear seat of his limousine during Dallas motorcade. Photo / AP

Former Washington Post editor and author of The Ghost, Jefferson Morley hopes the files reveal new information about spymaster James Angleton, who he wrote his book about.

He believes the CIA covered up their knowledge of Oswald to protect themselves.

"Were they covering up a manipulation of Oswald, an operation to use him, or were they covering up their own incompetence? This guy came through, they were paying close attention to him and he up and shot the president.

"Those are the two possibilities and the information that we're going to get, if we get all of it, may shed real new light on this."