Ive always believed that he died during the jump, or shortly afterwards due to injuries. IIRC the serial numbers used on the ransom money cash have never showed up in circulation since the hijacking in 1971.
[quote name='']February 1980
Brian Ingram, an 8-year-old boy, finds $5,800 in decomposing $20 bills by the edge of the Columbia River near Vancouver, Washington. The FBI matches the serial numbers on those bills to the Cooper ransom. It is the only Cooper money ever to be recovered.
Brian Ingram, now 14, receives $2,760 from his discovery of the small portion of Cooper loot. An equal share is given to the insurer of Northwest Orient. The last $280 is kept as evidence.[/quote]