Washington (AFP) - A new trove of secret files related to the November 1963 assassination of US president John F. Kennedy was released on Thursday, but the White House held thousands of documents back, citing national security concerns.

The Warren Commission that investigated the shooting of the charismatic 46-year-old president determined that it was carried out by a former Marine sharpshooter, Lee Harvey Oswald, acting alone.

That formal conclusion has done little, however, to quell speculation that a more sinister plot was behind Kennedy’s November 22, 1963 murder in Dallas, Texas, and the painstaking release of the government files has added fuel to various conspiracy theories.

The National Archives said a total of 13,173 documents had been made public on Thursday in the latest release, and that 97 percent of the Kennedy records – which total approximately five million pages – have now been made public.

President Joe Biden said in a memorandum that a “limited” number of documents would continue to be held back at the request of unspecified “agencies.”

Previous requests to withhold documents have come from the Central Intelligence Agency and the Federal Bureau of Investigation.

“Temporary continued postponement of public disclosure of such information is necessary to protect against an identifiable harm to the military defense, intelligence operations, law enforcement, or the conduct of foreign relations,” Biden said.

Kennedy scholars have said the documents still held by the archives are unlikely to contain any bombshell revelations or put to rest the rampant conspiracy theories about the assassination of the 35th US president.

Oswald was shot to death two days after killing Kennedy by a nightclub owner, Jack Ruby, as he was being transferred from the city jail.

- Oswald and the KGB -

A significant number of the files released on Thursday related to Oswald, his international travel and contacts in the weeks, months and years ahead of the Kennedy assassination.

Oswald defected to the Soviet Union in 1959 but returned to the United States in 1962.

Among the documents released on Thursday was one from 1990 that recounts the debriefing of a former KGB officer who said Oswald was recruited by the KGB after defecting, but he was considered “a bit crazy and unpredictable.”

The officer said the KGB had no further contact with Oswald after he returned to the United States suffering from depression and homesickness, and the KGB “never tasked him to kill President Kennedy.”

Another document, from 1991, cites a different KGB source as saying that Oswald was “at no time an agent controlled by the KGB” although the KGB “watched him closely and constantly while he was in the USSR.”

Hundreds of books and movies such as the 1991 Oliver Stone film “JFK” have fueled the conspiracy industry, pointing the finger at Cold War rivals the Soviet Union or Cuba, the Mafia and even Kennedy’s vice president, Lyndon Johnson.

The release of the documents is in compliance with an October 26, 1992 act of Congress which required that the unredacted assassination records held in the National Archives be released in full 25 years later.

Thousands of Kennedy assassination-related documents from the National Archives were also released while Donald Trump was in office, but the former president also held some back on national security grounds.