The American intelligence community is bracing itself for a slew of new conspiracy theories and possible criticism over its handling of the assassination of President John F Kennedy in 1963.

A treasure trove of National Archive documents, sealed under a 1992 law, had been mandated to be released by October 26.

At the weekend, President Donald Trump announced on Twitter he did not plan to stand in the way of the scheduled release.

That includes 3000 documents that had never been seen by the public and more than 30,000 that had been released previously but with redactions.

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

Mr Trump had the power to block the release of the documents, and intelligence agencies are thought to have pressured him to do so for at least some of them.

The New York Times reported that researchers did not expect any bombshells that significantly alter the official narrative of the assassination — that Lee Harvey Oswald acted alone in Dallas — delivered in 1964 by the Warren Commission.

But the documents are likely to “help fuel a new generation of conspiracy theories”, according to two authors who have written about the assassination – Philip Shenon, a former New York Times reporter and Larry J Sabato, a University of Virginia professor.

Both have pointed to a mysterious chapter in the history of the assassination – a six-day trip that JFK assassin Oswald paid to Mexico City several weeks before the president’s murder, in which Oswald met with Cuban and Soviet spies and came under intensive surveillance by the CIA’s Mexico City station.

Previously released FBI documents suggest that Oswald spoke openly in Mexico about his intention to kill Kennedy.

“It’s going to be very interesting to see what else the government knew about the threat Oswald might pose — how much more they learned about his trip in Mexico City and whether or not they bungled evidence to suggest he was a threat,” Mr Shenon told the ABC.

Trump has invoked conspiracy theories

Conspiracy theorists have long looked for evidence to prove the US government covered up the truth about the assassination.

Mr Trump is no stranger to conspiracy theories, including those involving the Kennedy assassination.

Lee Harvey Oswald holds a rifle in an undated Dallas Police Department archive image.

During the presidential campaign, he at one point alleged that the father of Senator Ted Cruz, a Republican primary rival from Texas, had been with Oswald shortly before Kennedy was killed.

“You know, his father was with Lee Harvey Oswald prior to Oswald’s being, you know, shot,” Mr Trump told Fox News in an interview in May 2016, as he battled the Texas senator for the nomination.

“I mean, the whole thing is ridiculous. What is this, right, prior to his being shot, and nobody brings it up. They don’t even talk about that. That was reported and nobody talks about it. But I think it’s horrible.”

He went on: “What was he doing with Lee Harvey Oswald shortly before the death, before the shooting? It’s horrible.”

Mr Trump has at times dabbled in other conspiracy theories: He once seemed to consider the possibility that Justice Antonin Scalia had been murdered and for years, he was the most vocal purveyor of the falsehood that former president Barack Obama was born outside the United States.

Americans are suspicious of the official story

On November 22, 1963, Kennedy was shot in the head and neck as he rode through Dallas in an open car. The Warren Commission was formed just a week afterwards to officially examine what happened.

The following September, it issued an 888-page report with 26 volumes of supporting material. It found that Oswald, who was shot and killed by Texas nightclub owner Jack Ruby two days after Kennedy’s assassination, acted alone when he mortally wounded the 35th president.

However, in 2013, a Gallop poll found that only 30 per cent of Americans believed that Oswald was the lone gunman.

Some have argued the CIA played a part, while others have pointed the finger at organised crime or then-Cuban president Fidel Castro.

A Trump political ally Roger Stone wrote a book in 2013 entitled The Man Who Killed Kennedy: The Case Against LBJ.

Mr Stone claimed to prove that Lyndon B Johnson, Mr Kennedy’s vice-president who became president upon his death, was “not only involved in JFK’s assassination, but was in fact the mastermind”.

Who is unhappy about the release of the Classified JFK files ! The Bush Crime Family , Ted Cruz's creepy father and LBJ greedy daughters !

— Roger Stone (@RogerJStoneJr) October 21, 2017

Last week, Mr Stone told far-right conspiracy theorist and radio show host Alex Jones that he had personally urged the President to make the JFK files public.

He added that “a very good White House source”, but not Mr Trump, had told him the Central Intelligence Agency, and specifically its director Mike Pompeo, had been “lobbying the President furiously not to release these documents”.

“Why? Because I believe they show that Oswald was trained, nurtured and put in place by the Central Intelligence Agency. It sheds very bad light on the deep state.”

– with agencies