WASHINGTON — Mohammed Rashed slipped a bomb beneath the jetliner seat cushion, set the timer and disembarked with his wife and child when the plane landed in Tokyo. The device exploded as Pan Am Flight 830 continued on to Honolulu, killing a Japanese teenager in a 1982 attack that investigators linked to a terrorist organization known for making sophisticated bombs.

It would be 20 years before the bomber — and one-time apprentice to Abu Ibrahim, currently featured on the FBI list of most wanted terrorists — would admit guilt in an American courtroom.

Now, credited for his cooperation against associates, Rashed will be released from federal prison within days after more than two decades in custody in Greece and the United States....