Updated 8 a.m. Saturday: Trump announced he will release the remaining documents.

WASHINGTON — Generations of professional and amateur sleuths have spent decades steeped in the details of the JFK assassination. In coming days, they’ll be able to pore through thousands more files kept classified for 54 years.

On Saturday morning, President Donald Trump announced on Twitter that he will authorize release of the remaining documents.

"Subject to the receipt of further information, I will be allowing, as President, the long blocked and classified JFK FILES to be opened," he tweeted.

Subject to the receipt of further information, I will be allowing, as President, the long blocked and classified JFK FILES to be opened. — Donald J. Trump (@realDonaldTrump) October 21, 2017

Hours later, the White House issued this statement: "The President believes that these documents should be made available in the interests of full transparency unless agencies provide a compelling and clear national security or law enforcement justification otherwise."

Those who are sure that Lee Harvey Oswald acted alone are eager for vindication and new jigsaw pieces to fill the void spots in the puzzle. So are those who blame the mob, Fidel Castro, the Soviets or the military-industrial complex.

Lost on neither camp is the fact that the authority to decide which secrets to keep sealed for another decade or more rests with a president known for indulging conspiracy theories.

Archivist Ken Hawkins looked over files concerning the assassination of President John F. Kennedy in May 1994 at the National Archives in College Park, Md. (Marcy Nighswander / The Associated Press)

The deadline is Oct. 26, set by Congress a quarter-century ago after Oliver Stone’s conspiracy-minded JFK movie reignited demands to open the files on John F. Kennedy’s murder in Dallas on Nov. 22, 1963.

By coincidence, Trump plans to be in Dallas for a campaign fundraiser on Wednesday — the day before the deadline.

Anyone who expects a holy grail, a document that spells out exactly what happened to the 35th president, who did it and who could have stopped it, will probably be disappointed, however many of the 3,100 remaining files Trump allows the National Archives to unveil. The wording of Trump's announcement on Saturday morning left open the possibility of a last-ditch push by the CIA or another agency to block some material.

Still, said John Tunheim, who led the panel Congress created in 1992 to review and release the files, “Everything should come out. ... I can’t believe we’d be compromising anything from the 1950s and 1960s.”

His view: Oswald was the lone gunman, though he could have had help — and we may never know.

“I don’t think there are big revelations,” said Tunheim, now the chief U.S. district judge for Minnesota, adding that he’s sure secrets have been kept too long.

“We as a government created a lot of the mistrust of government surrounding the Kennedy assassination by protecting way too much information.”

He’s not alone in seeing little hope for a major breakthrough. Still, researchers will remain nervous until the remaining cache is unsealed.

"My guess is if there ever were telltale documents, they were destroyed long ago," said Larry Sabato, director of the University of Virginia Center for Politics and author of The Kennedy Half-Century. "It's been 54 years. Really. If they add another 25 years? I don't think anybody who lived through it as an adult will be around if it doesn't come out now."

Artifacts from the Kennedy assassination that are preserved in the National Archives include (clockwise from left): The bloodstained outfit Jacqueline Kennedy refused to change out of until her return to Washington; a bullet found on a stretcher at Parkland Memorial Hospital where President Kennedy was taken; a bullet hole in the shirt Lee Harvey Oswald was wearing when he was killed by Jack Ruby; the dictabelt from a Dallas police motorcycle that recorded audio of the assassination; and the movie camera used by Abraham Zapruder when he filmed the moment of Kennedy's death. (The Associated Press (left) and The National Archives)

What the documents may show

Most of the 5 million pages of Kennedy records were released in the 1990s, a bonanza for assassination buffs on a host of related topics, including plots against Cuban dictator Castro and monitoring of anti-war groups, the Rev. Martin Luther King Jr., the Weathermen and others.

The National Archives released more material in July, including thousands of files kept classified until now by the Assassination Records Review Board. Some of the material had faded to the point it was no longer readable.

Congress created the five-member review board in 1992 as part of a law requiring the release of all Kennedy assassination documents within 25 years. Only the president can block release, if he deems it would harm U.S. intelligence, law enforcement, military or diplomacy interests.

Dallas Morning News archives

Oct. 26 is the law’s 25th anniversary. Archivists have been scrambling for months, awaiting the go-ahead from the president.

Trump aides didn't clarify Saturday whether he intends to keep any records classified, and archives officials haven't announced a time table for release.

White House spokeswoman Lindsay Walters said Thursday that the administration had been working with the National Archives and assorted federal agencies "to ensure that the maximum amount of data can be released to the public," balancing a goal of "providing the full historical record while protecting national security by ensuring against identifiable harm to current military defense, intelligence operations, law enforcement, or conduct of foreign relations."

The files due for release contain hundreds of thousands of pages, mostly from the CIA and FBI. The review board weighed 27,000 requests to withhold information. It released some files with names or code names of agents and operations blacked out. Historians and authors are eager for the unredacted versions.

“There’s no Star Chamber report,” said Rex Bradford, president of the Mary Ferrell Foundation, which has posted a searchable archive of the JFK material online to make research easier. But “there are documents I am looking forward to seeing. ... It’s been peeling an onion for five decades. The bulk will be pretty impressive, if it happens.”

In 2013, to observe the 50th anniversary of President John F. Kennedy's death in Dallas, the National Archives digitized many materials relating to his assassination. These Dallas Police Department booking photos of Lee Harvey Oswald, taken Nov. 23, 1963, are among the images that had previously only been available in hard copy form. (Warren Commission, Aubrey Lewis Exhibit 1) (National Archives)

The trove still under seal is believed to include a CIA personality study of Oswald, top-secret congressional testimony of former CIA officers, letters from longtime FBI director J. Edgar Hoover and from widowed first lady Jackie Kennedy, the CIA file on an attorney for New Orleans mobster Carlos Marcello (the man behind the assassination, if you buy that particular theory), and a file on E. Howard Hunt, one of the Watergate burglars.

There may also be revelations from interrogations with Yuri Nosenko, a KGB agent who defected to the United States in 1964. Some of the transcripts and recordings have already been released.

Oswald defected to the Soviet Union in 1959 and lived in Minsk for 2 1/2 years. Nosenko, who died in 2008, told his U.S. handlers that he had dug through Oswald's file and assured them that Oswald had never been a Soviet agent, having been deemed too unstable and untrustworthy.

There's also the personnel file on George E. Joannides, the CIA officer assigned in 1978 as the agency's liaison to the House Select Committee on Assassinations. It wasn't until 2001 that a researcher discovered he was the same officer who had overseen Cuban dissidents in 1963 from Miami, under a pseudonym. That fueled fresh conspiracy theories, raising questions about whether his mission was to ensure that Congress didn't learn too much.

The big prize about to be released may be material related to Oswald’s trip to Mexico City seven weeks before the assassination.

It’s “one of the keys to this whole affair,” said Bradford.

Warren Commission Exhibits 2966a and Exhibit 2966b: Lee Harvey Oswald distributing "Fair Play for Cuba" handbills in New Orleans on Aug. 16, 1963. Insets show samples of his handbills, on which he had stamped his name and the name of A.J. Hidell. (Warren Commission)

The CIA had Oswald under surveillance. Thanks to cooperation from Mexico, the Americans had bugged the Soviet and Cuban embassies, where Oswald sought a visa in order to return to the Soviet Union. (The material had been kept sealed over concern that Mexico’s ruling party would face backlash for working so closely with U.S. intelligence.)

Records already uncovered provide tantalizing — if disputed — hints that Oswald was overheard vowing to kill Kennedy, possibly in hopes that would impress the Soviets.

The judge doesn’t recall any death threat by Oswald in the files.

"If he uttered some kind of threat, we would have released that," Judge Tunheim said.

The Dallas FBI office had been keeping an eye on Oswald, but the CIA never told the bureau about the Mexico trip, said Hugh Aynesworth, a longtime Dallas journalist who authored November 22, 1963: Witness to History. He's a leading figure in the Oswald-acted-alone camp.

“CIA and the FBI tried to cover their butts,” Aynesworth said, adding that when all the records come out, “they’re going to be embarrassed. ... They covered up mistakes and lied about who knew what and when.”

But, he added, “you’re not going to find any second assassin. ... I’d bet my life.”

Skepticism persists, authority rests with Trump

That’s the official story, that Oswald acted alone.

A week after the assassination, Texan Lyndon Johnson — sworn in as president aboard Air Force One at Dallas Love Field with a blood-spattered Jackie Kennedy at his side — named Chief Justice Earl Warren to lead the inquiry.

The 888-page Warren Commission report, completed 10 months later, found that Oswald bore sole responsibility.

A Gallup poll four years ago, timed to the 50th anniversary of the assassination, found that only 30 percent of Americans believe that. Most believe a conspiracy of some sort led to Kennedy's death.

Judge Sarah T. Hughes administered the presidential oath to Lyndon Johnson aboard Air Force One at Love Field after Kennedy's death. Johnson's wife, Lady Bird (background) and the slain president's widow, Jackie Kennedy, were among the witnesses. (Cecil Stoughton / The White House)

SOURCE: Gallup poll released Nov. 13, 2013

But while skepticism remains strong, it has steadily eroded.

At various points in the last five decades, as many as 4 in 5 Americans believed that JFK died as the result of a conspiracy. In the public mind, suspicion falls on organized crime, “the government,” the CIA, Castro and others.

The documents yet to be unsealed probably won’t settle any of this.

Trump has reportedly been lobbied by trusted associates on both sides.

Roger Stone has pushed the theory that Johnson masterminded the plot to kill Kennedy. (Mark Wilson / Getty Images)

His CIA director, Mike Pompeo, has pressed to keep portions of the trove classified. Roger Stone, a longtime adviser who maintains that Kennedy’s vice president, Johnson, masterminded the plot, has urged full disclosure.

Trump’s theories remain a mystery. His tweets and public statements through the years hold no clues.

He has shown an unusual willingness to promote conspiracy theories.

The president maintained for years, despite strong evidence to the contrary, that President Barack Obama's Hawaii birth certificate was forged. During the 2016 campaign, he peddled the unfounded theory that Sen. Ted Cruz's father had associated with Oswald; he cited a supermarket tabloid that had reproduced a grainy picture of Oswald and a man who bore little resemblance to the elder Cruz.

“He’s a classic conspiracy theorist. He spins the tales himself as he did with Ted Cruz’s dad,” Sabato said.

The CIA won’t confirm whether it has been pushing to keep any documents classified, nor will it discuss the nature of the secrets it’s been keeping for decades.

“CIA continues to engage in the process to determine the appropriate next steps with respect to any previously unreleased CIA information,” spokeswoman Nicole de Haay said Monday — the same stance, verbatim, that the agency has maintained for weeks as the deadline looms.

Stone told conspiracy site Infowars this week that he has been lobbying Trump to release all of the documents. He has speculated that they will support the conclusions in his 2013 book, The Man Who Killed Kennedy: The Case Against LBJ, which argues that Johnson conspired with the CIA, organized crime and oil interests to assassinate the president.

“I know CIA Director Pompeo is urging the president to delay release of these records for another 25 years,” Stone said this month. “They must reflect badly on the CIA even though virtually everyone involved is long dead.”

Author Gerald Posner has joined with Stone in demanding release of the files, though his views of the case are the complete opposite. His book, Case Closed: Lee Harvey Oswald and the Assassination of JFK, affirmed the Warren Commission's findings that Oswald acted alone.

Hell must have frozen over. @RogerJStoneJr and I on the same side of JFK assassination. Well, at least when it comes to releasing ALL the JFK files this Oct 26. If not, @POTUS must free them. #CaseClosed. @WarRoomShow https://t.co/kRXsAqowdv pic.twitter.com/yYhVeP07pu — Gerald Posner (@geraldposner) October 3, 2017

"These files should have been released long ago,” Posner said this month, complaining that “under the guise of national security,” the government had held documents under seal for far too long. “All the secrecy just feeds people’s suspicions that the government has something to hide and adds fuel to conspiracy theories.”

Although the review board’s mission was never to reinvestigate the crime, its members developed expertise matched by few researchers. Tunheim, like Sabato and the Warren Commission, points to Oswald, though he has questions about nightclub owner Jack Ruby, who ended up killing the assassin.

“I see all of the evidence pointing toward Oswald as being the lone shooter,” Tunheim said. “Could there have been a second shooter? Could there have been a conspiracy? Certainly. ...

“But,” he continued, “I deal in hard evidence that can be brought into court. It was his gun, his prints all over it. The shells matched the bullets in the car. Everything points to Oswald doing it.”

That said, the review board interviewed everyone who worked for the House Select Committee on Assassinations in the late 1970s.

“To a person,” Tunheim recalled, “they said that they believed that organized crime was involved in the conspiracy. But also to a person, they said: `We could not prove it. We tried very hard and could not prove it.’ I don’t know that we’ll ever know all the answers.”