the FBI officially closed active investigation on this one in 2016, still unsolved, first time they've given up on it.
hijacked a plane in 1971, got $200k ransom, and parachuted out over Washington state mid-flight, never identified, never found. still the only unsolved plane hijacking in US history, people are obsessed with this case.
part of his ransom money was actually found years later, buried in sand along a riverbank, but it never led anywhere in identifying him.