The US National Archives on Thursday released thousands of documents related to the 1963 assassination of then President John F Kennedy shortly after Joe Biden issued an executive order authorizing the release that also kept hundreds of other sensitive records secret.

The release of 12,879 documents was not expected to include any new bombshells or change the conclusion reached by the commission led by chief justice Earl Warren that Lee Harvey Oswald, a former Marine and communist activist who had lived in the Soviet Union, acted alone. However, the latest cache will be useful for historians focusing on the events around the assassination.

Kennedy was shot and killed while riding in his motorcade through Dallas on 22 November 1963, at the age of 46.

Thousands of books, articles, TV shows and films have explored the idea that Kennedy’s assassination was the result of an elaborate conspiracy. None have produced conclusive proof that Oswald – who was fatally shot by nightclub owner Jack Ruby two days after killing Kennedy – worked with anyone else, although they retain a powerful cultural currency.

There were initial concerns that Ruby might have had some connection to Oswald. But a newly released September 1964 memo to the presidential commission investigating the assassination said “the Central Intelligence Agency has no indication that Ruby and Lee Harvey Oswald ever knew each other, were associated, or might have been connected in any manner”.

Congress in 1992 had ordered that all remaining sealed files pertaining to the investigation into Kennedy’s death should be fully opened to the public through the National Archives in 25 years, by 26 October 2017, except for those the president authorized for further withholding.

In 2017, then President Donald Trump released a cache of records, but decided to release the remaining documents on a rolling basis.

All of the remaining JFK files were originally supposed to have been released in October 2021. Biden postponed that planned release, citing delays caused by the Covid-19 pandemic, and announced they would be instead disclosed in two batches: one on 15 December 2021, and another by 15 December 2022, after undergoing an intensive one-year review.

With Thursday’s release, 95% of the documents in the CIA’s JFK assassination records collection will have been released in their entirety, a CIA spokesperson said in a statement, and no documents will remain redacted or withheld in full after an “intensive one-year review” of all previously unreleased information.

In a memorandum on Thursday, Biden said that until 1 May 2023, the National Archives and relevant agencies “shall jointly review the remaining redactions in the records that had not been publicly disclosed”. After that review, “any information withheld from public disclosure that agencies do not recommend for continued postponement” will be released by 30 June 2023.