ABC News’ Jack Cloherty reports:

Nearly 48 years after the assassination of President John F. Kennedy, fresh audio evidence from that fateful day has surfaced.  The evidence comes in the form of the original reel-to-reel Air Force One radio recording, containing conversations between officials on the plane, the White House situation room, and others.  The original tape was long thought to be lost or destroyed.

The tape contains never-before-heard conversations between the presidential aircraft and the White House and immediately after the assassination of President Kennedy on Nov. 22, 1963.

It was held privately for years by President Kennedy’s military aide at the time, Chester Clifton.  Clifton was in the Dallas motorcade when Kennedy was shot and killed, and on Air Force One and involved in the radio discussions.  The tape was obtained by the Raab Collection of Philadelphia.

According to Nathan Raab, the Vice President of the collection, the tape is the raw, unedited version of the edited audio tape from Air Force One that is in the National Archive.  The Raab Collection says the raw tape “is about 30 minutes longer than the edited version, predates it by years, and contains incidents and code names never before heard by the American public.”

“That this tape even exists will change the way we view this great event in history,” said Raab. “It took decades to analyze the shorter, newer version and it will take years to do the same here. This provides a concise ‘tale of the tapes’ and offers great insight into ongoing research.”

The tape contains a dramatic first-hand report of the President’s assassination, and the wounding of then-Texas Governor John Connolly.  The recordings may fill in some important blanks for the assassination historians and conspiracy theorists – for example, the tapes locate Gen. Curtis LeMay at the time of the assassination.   LeMay, a member of the Joints Chiefs of Staff, was a vocal critic of JFK and there has been speculation over the years that he may have had a role in the assassination.  The tapes also placed various other officials, allowing the public to learn where they were, at what time, and what they were saying.

Listen here.

Much of the recording involves logistical planning – whether to take the President’s body for autopsy to Walter Reed or Bethesda Naval Hospital; plans for where Mrs. Kennedy should be taken, and how many limousines should meet the plane when it touched down.

“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,” Nathan Raab, said.   ”This longer, more complete tape is a crucial discovery, and a landmark piece of American history.”

Raab said the collection is offering the original, reel-to-reel tape for sale at $500,000.  A digital file will be provided at no cost to the National Archives and John F. Kennedy Library.