The crash killed 11 people in Lockerbie

A painstaking operation was mounted to recover the wreckage which was strewn over a huge area. Experts pored over tiny pieces of debris, reconstructed part of the shattered Boeing jumbo jet and tried to work out exactly where the bomb had been placed.

At first the police investigation focused on the activities of a Syrian-backed extremist Palestinian group - the Popular Front for the Liberation of Palestine-General Command - especially on a cell uncovered in Germany.

Iranian connection

Stories have surfaced over the years suggesting that the Islamic Iranian Government was responsible - acting to avenge the loss of one of its airliners which was shot down by the US over the Gulf a few months before Lockerbie.

But the official investigation took another turn. In November 1991, Scottish prosecutors charged two alleged Libyan intelligence agents, Abdelbaset Ali Mohmed Al Megrahi, and Al Amin Khalifa Fhimah, with carrying out the bomb attack.

Cleared: Al Amin Khalifa Fhimah

From that point, the story turned into a diplomatic confrontation between Libya and the United Nations Security Council.

Backed up by France, which held Libya to blame for a separate bomb attack on a French airliner over the Sahara, the United States and Britain pushed a resolution through the security council calling on Libya to co-operate with Western judicial authorities.

In effect, that meant handing over the suspects for trial. When Libya refused, the UN imposed limited sanctions, including an air embargo and a ban on the supply of equipment for the Libyan oil industry.

Several years of stalemate followed, while the families of the American and British victims of the Lockerbie attack wondered if they would ever discover the truth or see anyone brought to trial.

Colonel Gaddafi made various offers, usually vague - that Libya might try the two accused itself; that they might give themselves up voluntarily; that an international court might be convened. None was acceptable to Washington or London.

Guilty: Abdelbaset Ali Mohmed Al Megrahi

But in 1998, almost 10 years on, things began to move.

In April, the Libyans told representatives of the families that they would hand over the two men for trial in a third country under Scottish law.

In July the British and American governments said they were exploring a similar idea, reversing their position that a trial could take place only in Scotland or the United States.

One reason for the shift was growing breaches of the air embargo by African leaders. Another was the determination of the new Labour government in Britain to break the deadlock.

Trial

It took many more months to finalise an agreement. Various mediators were involved in the negotiations - the UN Secretary-General, Kofi Annan, Nelson Mandela and envoys from Saudi Arabia.

At last, Libya agreed that if convicted the two accused would serve their life sentences in Scotland, although the trial would be held in the Netherlands.

And it accepted assurances that they would not be interrogated by Western intelligence or spirited away to Washington.

In a dramatic operation in April 1999, the two Libyans were flown into a former Dutch military base at Camp Zeist. As part of the deal, UN sanctions were suspended, though not finally lifted.

Outcome

The trial finally got under way at Camp Zeist, in a specially built, ultra-modern court, in May last year.

It has been a unique event - the product of an elaborate compromise reflecting the fact that there is at present no permanent international criminal court to try cases of this kind.

It has been an extremely complex case with a lot at stake.

Despite the verdicts, future relations between Libya and the West, and the peace of mind of the victims' families, are still unresolved.