Two possibilities: Only 'Dan Cooper' knew, or only the FBI knows. If the FBI recovered the briefcase with the 'bomb', they would likely keep this information secret to aid in investigating suspects, which they are still doing.
The fact there is no mention in public records of the whereabouts or disappearance of the briefcase with the 'bomb' could indicate: A. The FBI has it, or B. Cooper dumped it out the rear door of the plane (possibly a while) before he jumped, and it was never found.
I think B is more likely, since Cooper seemed to be a careful planner, and he would want to eliminate as much evidence as possible.
DB Cooper was 43 when we first heard his name
DB Cooper was famous for hijacking a commercial airplane in 1971, extorting a ransom of $200,000, and parachuting out over the Pacific Northwest. He remains one of the most elusive and mysterious criminals in US history, as his real identity and whereabouts were never discovered.
The Man Who Found DB Cooper - 2012 was released on: USA: 23 April 2012
DB Cooper
No one really knows
Yes, D.B. Cooper was a real person. He hijacked a Boeing 727 aircraft in 1971, demanded a ransom, then parachuted out of the plane never to be caught. The FBI conducted an extensive investigation but his true identity and whereabouts remain unknown.
No one knows if Dan cooper is a real or made up name. I think it is a made up name because i don't think he would take the chance of being traced. So to answer your question no one really knows.
No one knows. He was never found.
No one knows. He was never found.
No one knows. He was never caught.
D.B. Cooper jumped out of a Boeing 727 airplane with $200,000 cash
Miles Cooper letter bomb campaign happened in 2007.