Officials in Dallas, Texas, have unveiled the purported transcript of a conversation between US President John F Kennedy's assassin and another man.
The purported transcript may re-open the JFK conspiracy debate
The transcript records an alleged conversation between assassin Lee Harvey Oswald and Jack Ruby, who killed Oswald before he could face trial.
The two men discuss a plot to kill the president a month before his 22 November 1963 murder in Dallas.
A Dallas official said he did not know whether the transcript was genuine.
The transcript was found in a Dallas courthouse safe with other papers related to the assassination.
Dallas County District Attorney Craig Watkins said he was told about the contents of the safe when he took office in 2007.
He showed a news conference the alleged transcript, a leather gun holster used to carry the gun that Ruby shot Oswald with, and a movie contract signed by Henry Wade - the Dallas District Attorney when Mr Kennedy was killed.
"We don't know if this is an actual conversation or not," said Mr Watkins.
President Kennedy was shot as he rode in an open-topped car
"It will open up the debate as to whether or not there was a conspiracy to assassinate the president."
Staff at Mr Watkins' office have been busy cataloguing the items since the safe was opened last year.
One theory is that the transcript is a fake - part of a movie script that Mr Wade was working on.
In the transcript, Oswald and Ruby discuss a way to "get rid of" US Attorney General Robert Kennedy - JFK's brother - by killing the president.
Robert Kennedy was launching a crackdown on the mafia in the US at the time.
The conversation purportedly took place at a nightclub in Dallas owned by Ruby.
An investigation by the Warren Commission into the Kennedy assassination maintained that Oswald probably acted alone, although other inquiries challenged this conclusion.