Abdel Baset Ali al-Megrahi was an intelligence agent. Since he worked for the Libyan Government, he probably did some bad things.

But he probably did not do the specific bad thing for which he was sentenced to 27 years in prison in Scotland.

He only served eight years. He was released on compassionate grounds last Thursday by the Scottish Justice Secretary, Kenny MacAskill, and flew home to Libya.

He is dying of cancer, but his release outraged the Americans whose relatives died aboard Pan Am Flight 103 in December 1988. They believe that al-Megrahi is a mass murderer who should die in jail - but that is not necessarily so.

There were also British victims of the attack, and almost none of their relatives think that al-Megrahi should have been in jail at all. As their spokesman, Jim Swire, put it: "I don't believe for a moment that this man was involved [in the bombing]."

Back in 1988-89, Western intelligence services saw the bombing of Pan Am 103 as an act of revenge. The US warship Vincennes had shot down an Iranian Airbus five months before, killing all 290 passengers, and the Iranians were getting even.

(The US was then secretly backing Saddam Hussein's war against Iran, and the Vincennes, operating illegally in Iranian territorial waters, shot down the airliner thinking that it was an Iranian fighter.)

There was some evidence for this "Iranian revenge" theory. In 1989 German police found the same kind of bomb that brought down Pan Am 103 in a house in Frankfurt that were used by the Popular Front for the Liberation of Palestine - General Command. This organisation was based in Syria, and Syria and Iran were allies, so maybe ...

But then, in 1990, Saddam Hussein invaded Kuwait. Washington needed Arab countries like Syria to join the war against Saddam so the liberation of Kuwait looked like a truly international effort. Syria's price for sending troops was removal from America's most-wanted list. Suddenly Syria was no longer the prime suspect in the Pan Am case - and if Syria was out, so was Iran.

But more Americans died on Pan Am 103 than in any other terrorist attack before 9/11. Somebody had to take the fall. Libya was the obvious candidate, because it had supported various terrorist attacks in the past.

Soon new evidence began to appear. It pointed to al-Megrahi, who had been working as a security officer for Libyan Arab Airlines in Malta in 1988. A Maltese shopkeeper identified him as the man who bought children's clothing like that found in the suitcase that contained the bomb that brought down Pan Am 103.