Diplomats say the vanished hijackers of Kuwait Airways Flight 422 will most likely end up in Moslem west Beirut, but U.S. officials want the air pirates punished and suspect one of them may have killed an American during a 1985 hijacking.

The hijackers' whereabouts remained a mystery Thursday, 24 hours after they freed their last 31 hostages to end a 16-day, 7,600-mile odyssey of terror in which two Kuwaiti captives were killed.In Washington, the State Department said it has indications that one of the hijackers also was involved in the 1985 hijacking of a TWA airliner and the killing of one of its passengers, U.S. Navy diver Robert Stethem.

Department spokeswoman Phyllis Oakley identified the hijacker as Hassan Izz-al-din, who is wanted under an existing U.S. arrest warrant.

"He was directly involved in the murder of Robert Dean Stethem aboard TWA (Flight) 847, and we want him brought to justice," she said. "As long as he is free, there is a real and considerable risk that he will murder again, as he may have done in this case."

Oakley said the United States had no information about the arrangements that led to the hostages' release and declined to give specific details on whether the United States knew of the hijackers' whereabouts.

She said "we're inclined to believe" the hijackers are members of the pro-Iranian Hezbollah, or Party of God, which is based in Beirut.

Diplomatic sources said Wednesday the hijackers' most likely destination was Moslem west Beirut.

Before releasing the hostages early Wednesday, the hijackers issued a statement vowing not to give up their quest to win freedom for the 17 terrorists jailed in Kuwait for bombing the U.S. and French embassies in 1983.

A senior Kuwaiti official said Kuwait offered no concessions to the hijackers.

Kuwaiti sources close to a Kuwaiti delegation in Algiers said the sky pirates were "flown out to an undisclosed destination" aboard a special plane provided for under an Algerian guarantee of safe passage.

NBC News Wednesday night quoted Lebanese sources as saying the hijackers were still in Algiers and would leave the country "one by one." It also quoted U.S. officials as saying that before the release of the hostages Kuwait provided photographs and tapes of the 17 jailed bombing suspects to show they had not been harmed during their imprisonment.