Transcript for JFK assassination investigation files released
Reporter: More than 50 years after that tragic day in Dallas, there's still no smoking gun. Except for that .26-caliber rifle found on the sixth floor of the Texas school book depository, a rifle seen here in the hands of its owner, Lee Harvey Oswald. Among the thousands of classified documents finally unsealed last night by the national archives, there is nothing that would contradict the central finding of the Warren commission, that Oswald alone murdered America's 35th president. When I got and saw the documents and started to go through them, it became increasingly clear it was a nothing burger. This was very, very disappointed. Reporter: And yet some intriguing new details. Among them a reporter for an obscure British newspaper claims to have received advance warning of the assassination in a phone call supposedly a half hour before the fatal shots were fired. New questions about the CIA's role. New details about the possible motives of the Cubans to kill JFK. The documents also reveal how eager FBI director J. Edgar Hoover was to convince the public that Oswald is the real assassin. But the biggest hope for conspiracy theories and JFK obsessives may be president trump's 11th hour decision to delay the release of the most-sensitive documents by a further six months. Trump said he had no choice but to give the CIA and the FBI more time to review them. If there's a smoking gun in these JFK files, and I don't think there is, they're in the documents that are still being held back. Reporter: The jigsaw puzzle that has bedeviled this country for decades still has huge holes in it. President Kennedy has been shot in Dallas, Texas. Reporter: An overwhelming amount of evidence still points to the fact that Oswald pulled the trigger that day. Was he the lone gunman? Was he acting alone? Or were there others who got away with murder? On the grassy knoll, or lurking somewhere in the shadowy background? Half a century later those types of conspiracy theories burn just as bright as the eternal flame at JFK's grave. Before we get into all that -- ??? let's set the scene here. We're talking about camelot. Although the president is running behind schedule, he pauses momentarily to shake a few hands. Reporter: A handsome young president and his glamorous wife Jackie Kennedy, just 34 years old in that pink suit and pillbox hat in Dallas. A generation of Americans remember exactly where they were when Walter Cronkite delivered the tragic news. From Dallas, Texas, the flash apparently official, president Kennedy died at 1:00 P.M. Central standard time. 2:00 eastern standard time. Some 38 minutes ago. People who have experienced the tragedy of 9/11 who were alive then understand what a terrible shock it was to the country. The assassination of John Kennedy in 1963 was as great a shock or greater. It affected every American in a way that was immediate. Shoot Kennedy coming up Houston, there's plenty of time -- Reporter: Oliver stone's blockbuster movie "JFK" stirred up huge interest in conspiracy theories. The magic bullet enters the president's back, headed downward at an angle of 17 degrees. It then moves upward in order to leave Kennedy's body from the front of his neck. Wound number two. Reporter: So much so that congress hoped to arm Americans with the facts. 25 years before trump, they passed a law requiring the declassification of the Kennedy assassination archives. Unless the president at that later time were to object. So what do the newly declassified files contain? There are some tantalizing tidbits. For one, the CIA's role in the assassination remains unclear. There's this secret defendant by the former CIA director Richard Helms. Asked point blank by the Warren commission, is there any information involved with the assassination of president Kennedy which in any way shows Lee Harvey Oswald was in some way a CIA agent or agent? The document ends there, suspiciously. No answers given. There's new details about CIA plots to kill Cuban leader Fidel Castro involving a poison skin diving suit and explosive seashe seashells, enlisting the help of the mafia to carry them out. Those CIA mafia plots have long been advanced as possible motive for Cuba to kill JFK. But a newly declassified draft report of the house committee on assassinations rebuts that possibility in granular detail. Camelot may be ancient history. But it's a chapter that continues to fascinate people. For young congressman Joe Kennedy of Massachusetts, it's a living legacy, one that he tries every day to live up to. You're what, 36 now? Yeah. You'll be just about the same age as JFK when he ran? A little bit younger. I got no plans on that. Reporter: Maybe not. But presidential politics is in his blood. This was a print that was given to me by my aunt. Robert Kennedy was your grandfather, John Kennedy your great uncle. Is it hard to walk in those shoes? You don't walk in those shoes. How do you possibly live up to what giants and titans have done? Reporter: He wasn't happy about the release of these files, understandably so, it's too personal. I absolutely tend toward eing said, it would have been nice if TRE were some communication between this administration and members of our family. Reporter: As for the rest, the documents the CIA now promises no document will be withheld in full. We've waited more than half a century, what's six months more? I'm David Wright for "Nightline"
This transcript has been automatically generated and may not be 100% accurate.