What are the secret John F. Kennedy assassination files set for release?

— -- President Donald Trump said he will allow the public release of thousands of long-secret documents about the assassination of President John F. Kennedy 54 years ago.

A White House official said later that the release of the files could be held up if national security or law enforcement agencies believe that is necessary. Unless the president formally objects to the release of the documents, they will become available to the public this Thursday.

What are the JFK assassination files?

More than 5 million pages of records related to Kennedy's murder on Nov. 22, 1963, in Dallas, including photos, films, sound recordings and artifacts are held by the National Archives.

About 88 percent of these records have been fully available to the public since the late 1990s, and another 11 percent have been released with sensitive portions removed, the National Archives says on its website.

Still secret are the remaining 1 percent of files.

But under a 1992 law on the JFK files, all records previously withheld either in part or in full are to be released on Oct. 26, 2017, unless the president authorizes that they be withheld longer.

What did the government know and when did it know it

Professor Larry Sabato, director of the Center for Politics at the University of Virginia, is among the scholars looking forward to the release of the remaining documents.

He told ABC News that while he doesn't expect the remaining files to answer every question, he hopes they will reveal "critical details" such as what government agencies did or did not know.

“Ever since the assassination, so many questions have risen that people want to see what the government knew and when they knew it,” Sabato said. “Unfortunately most of the government including the FBI and the CIA have been unwilling to provide the critical pieces of information.”

“What I am looking to find are critical details of parts of this story that we don’t understand,” Sabato said, noting as an example the question of whether various law enforcement and intelligence agencies knew and communicated with each other about the fact that a man who had previously defected to the Soviet Union, Lee Harvey Oswald, was working at a site on the president’s motorcade route.

“Unlike some, I don’t think we’re going to find a Rosetta stone that suddenly puts all the pieces together and identifies members of a plot, it just doesn’t happen that way,” Sabato told ABC News. “The important part is we the people have to know, it’s been 54 years since the assassination.”

“The most sensitive papers are being held until the last day,” he said. “We hope we can fill in some of the blanks and help people understand what did really happen on November 22nd.”

'The government isn't hiding anything'

The judge who headed a board that reviewed for release the huge number of assassination records said making them public lets Americans see that the government is being fully transparent about the assassination.

"As of today if we can say everything that has been found in government files has been released in full to the public, yeah, I think that goes at least partways to helping people understand that the government isn't hiding anything significant from them," said Chief Judge John Tunheim of the U.S. District Court of Minnesota, who chaired a records review board established by the 1992 law but which no longer operates.

The judge said that although the records board has been "very diligent" about finding and releasing records, "it is entirely possible something has been found since the 1990s that has been sent over to the National Archives which has cast a new light on the assassination."

Another scholar said he doubts that any of the still-classified Kennedy files would compromise national security if they were released.

“It’s hard to think the things that were in existence in the 1960s would today jeopardize national security or be too sensitive for release,” said Patrick Maney, a presidential historian and professor at Boston College.

The National Archives declined to comment and referred all inquiries to the White House.