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
The Man Who Found DB Cooper - 2012 was released on: USA: 23 April 2012
No one really knows
DB Cooper
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 caught.
No one knows. He was never found.
No one knows. He was never found.
D.B. Cooper jumped out of a Boeing 727 airplane with $200,000 cash
The cast of The Man Who Found DB Cooper - 2012 includes: Deven MacNair as Driver Tim Moran as D. B. Cooper Stephen Quadros as Sheriff John
Miles Cooper letter bomb campaign happened in 2007.
Dan cooper(alias) who after a miscommunication with the press and FBI was commonly known as DB whereabouts are a complete mystery. However there are several theories about what happened to him.