Almost 50 years after the November 22, 1963 assassination, a two hour and 22 minute reel was found among the personal effects of JFK's senior military aide, Major General Chester Clifton, who died in 1991.
The reel contains more than 30 minutes of previously unheard footage of conversations on board Air Force One as Kennedy's body was being transported back to Washington from Dallas.
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It includes new code names and incidents, including a private conversation by the head of the Secret Service, Jerry Behn, about where to take the body and plans for where the First Lady, Jacqueline Kennedy, would be taken.
There is also an urgent effort by an aide to Air Force chief of staff Curtis LeMay, a well-known hawk and Kennedy critic, to reach Clifton; and attempts to locate various congressmen from Texas.
The material was acquired by the Raab Collection, a rare documents dealer based in Philadelphia, who donated a digitized copy to the National Archives, made public at gpo.gov/fdsys.
Experts say the tapes will stir debate among conspiracy theorists, especially about LeMay, a major Kennedy adversary whose name was conspicuously missing from an edited version of the original tape.
"People have always wanted to know where was Curtis LeMay on the day Kennedy was shot and there have been mixed messages about it. This tape provides exactly where he was," Kennedy historian Douglas Brinkley told CNN.
The Raab Collection is looking to sell on the original box and tape -- which has a label reading "Radio Traffic involving AF-1 in flight from Dallas, Texas to Andrews AFB on November 22, 1963" -- for $500,000.
"As Americans have looked to the history of the Kennedy assassination in search of answers, somewhere in an attic there existed a tape, made years before the only known surviving version, of the conversations on Air Force One on that fateful day," vice-president Nathan Raab says in a sale flier.
"This longer, more complete tape is a crucial discovery, and a landmark piece of American history."
The recording is a longer, unedited version of audio produced by the library of president Lyndon Johnson, who succeeded Kennedy after the assassination.
