(CNN) -- A newly discovered version of recordings made aboard Air Force One in the wake of President John F. Kennedy's assassination is being offered for sale at $500,000, the dealer selling the tape said Tuesday.
This version has never before been heard by the public, Raab Collection Vice President Nathan Raab told CNN.
"It's exciting when you find something that's not only an antique but contributes to the historical record," Raab said.
The Raab Collection, a historic documents dealer in Philadelphia, said in a statement the recording is more than 30 minutes longer than the version at the National Archives and contains the names of people never before heard from in the aftermath of Kennedy's assassination on November 22, 1963.
The Raab Collection is selling the reel-to-reel recording for $500,000, but is providing a digital file at no cost to the National Archives and the John F. Kennedy Library in Boston.
The tape was purchased by the Raab Collection in the public sale of the estate of Army Gen. Chester "Ted" Clifton, Jr., who served as the senior military aide to Kennedy and then to President Lyndon B. Johnson. An image of the label on the tape's box, shown on the Raab Collection website, says "Radio Traffic involving AF-1 in flight from Dallas, Texas to Andrews AFB on November 22, 1963."
"For General Clifton," the label says. It says it was made by the White House Communications Agency.
At the time it was purchased, it was just a tape in a box, Nathan Raab said, but employees felt there was something more to it.
They had the tape digitized and analyzed and compared it to transcripts from the time of assassination.
"This is a subject that has been extensively studied and there's no shortage of information on this tape," Raab said.
A comparison of published works about the day of the assassination and previously known audio recordings from that day helped the company determine the true identity of the recording.