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 a federal prison in Colorado within days, after more than two decades in custody in Greece and the United States.
The release does more than spring loose a convicted terrorist. It also could deprive the government of a star witness in the event that Ibrahim, a Palestinian master bomb-maker who authorities say orchestrated the Pan Am attack and similar strikes around the world, is captured.
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A former top lieutenant, Rashed would be able to implicate Ibrahim as the architect of the attack and help establish his identity in case prosecutors ever bring him to the United States to face justice.
Once freed, it is not clear that he would continue cooperating, though the Justice Department says it has enough other evidence for a conviction.
‘‘They certainly could teach people coming along. Whether they would or not, of course, I don’t know. Their ability to make bombs go off is quite extraordinary,’’ said Bob Baer, a former top CIA officer who worked clandestinely in the Middle East.
Justice Department spokesman Dean Boyd said the charges against Ibrahim, who was indicted in 1987 along with Rashed and Rashed’s Austrian-born wife, remain active and that the government is still seeking his prosecution.
Boyd wouldn’t comment on the potential effect of Rashed’s release, but he noted that prosecutors indicted Ibrahim long before Rashed was in custody or had begun cooperating.
‘‘The Justice Department does not bring charges against a defendant unless it believes it has sufficient evidence to prove the defendant’s guilt beyond a reasonable doubt in a court of law,’’ he said in a statement.
Rashed’s 2002 guilty plea required him to give up information on other terror plots in exchange for a release date of March 20, 2013.
The agreement also stipulated that Rashed, a Jordanian-born Palestinian from Bethlehem, would be deported to a country of his choice upon his release.
His lawyer wouldn’t comment on Rashed’s plans. The US Bureau of Prisons, which lists Rashed as 63 years old, also declined to comment.
The plea deal reflects the balancing of two government interests that are sometimes in conflict: securing lengthy prison sentences for dangerous felons while also incentivizing their cooperation against higher-value targets through the prospect of an early release.
Though Ibrahim remains at large, Rashed’s cooperation has been extensive by some accounts, including providing information about a 1986 airplane explosion that killed four Americans and a 1982 Berlin restaurant bombing that killed a child, former Assistant US Attorney General David Kris wrote in a 2011 article for the Journal of National Security Law & Policy.