LONDON — Abdel Basset Ali al-Megrahi, the only person ever convicted of the bombing of flight Pan Am 103, was released from a Scottish prison Thursday. The announcement was made by Scotland's Justice Minister, Kenny MacAskill.

MacAskill said he was releasing Megrahi on "compassionate grounds." The convicted man has terminal prostate cancer and the current prognosis of his survival is three months or less. The justice minister told reporters the Scots "are a people who pride ourselves on our humanity." He added: "We believe justice be served but mercy be shown."

The decision was made in the face of intense private and public pressure from senior U.S. officials. Secretary of State Hillary Clinton lobbied against the release right up to the last minute. She told reporters yesterday, "It is inappropriate. I am very much against it. I take this very personally. I think it is absolutely wrong."

Last week, six U.S. senators including John Kerry and Ted Kennedy sent a letter to MacAskill demanding that Megrahi remain in prison.

The decision is just the latest moment of controversy in a two decades long saga.

Pan Am 103 was blown out of the skies over Lockerbie Scotland on Dec. 21, 1988. All 259 people aboard the plane and 11 on the ground were killed. Most of the victims were either American or British, and over the years a split has developed between the two sides over the way justice should be pursued. The split comes from two very understandable needs of the victims' families: the need for punishment and the need for truth. In this case these needs were in conflict. Most of the American families wanted punishment. Susan Cohen, whose daughter died in the atrocity, told the BBC last week, "Any letting out of Megrahi would be a disgrace. It makes me sick, and if there is a compassionate release then I think that is vile." Her view is typical among American families.

But Dr. Jim Swire, a Briton who also lost a daughter, believes Megrahi is innocent. "Two wrongs don't make a right," he told the BBC. "The horror of Lockerbie plus the horror of this man dying away from his family don't make one right."

Swire, heads the group representing victim families in Britain. Over the years, the retired physician has become a lightning rod for the anger of victims' families in the U.S. He is acutely aware of the distress his views cause. "I don't want to make life worse for those who lost family members but forgive me, I want the truth."

The Lockerbie case is a paradigm of the wise old saw, "justice delayed is justice denied."

It took more than a decade to investigate the crime, accuse Megrahi and one other Libyan, Lamin Khalifah Fhima, of perpetrating it and then bring them to trial.

At every stage of the process there were enough gaps in the facts made public to inspire not just the usual gaggle of conspiracy theorists — people who think that every nefarious event in the world is either the work of the Mossad or governments in thrall to the oil industry — but more thoughtful people who do not see the puzzle fitting together and who ask, not unreasonably, if Megrahi is a fall guy doesn't that mean the real criminals are walking free?

A quick summary of the case:

Initial suspicion for the crime fell on the Iranian government. It had motive: In the summer of 1988, an American warship, the USS Vincennes, on patrol in the Persian Gulf had blasted an Iranian civilian airliner out of the sky killing 290 people. Ayatollah Khomeini had vowed revenge.

It was believed that the job was contracted out to a radical Palestinian faction in Syria. For more than a year this was the theory of the crime and FBI investigators were happy to leak the theory to the press.

Two years later, the theory changed. A scrap of clothing found at the site of the disaster, believed to have been in the suitcase which contained the bomb was traced to a store in Malta. The store's owner, identified Megrahi as the purchaser of the clothing. Megrahi worked for Libyan airlines in Malta.

The theory now shifted, Megrahi had put the bomb in a suitcase on a plane in Malta bound for Frankfurt. In Frankfurt, the suitcase was put on a Pan Am flight 103A to London, there the bag was transferred on to Pan Am 103 to New York.

Libya's motive for the attack was not clear.

Warrants were issued for Megrahi's and Fhimah's arrest in 1991. It would take six years and a change of British government before Nelson Mandela was able to broker a deal between the new British prime Minister, Tony Blair, and Libyan dictator Moammar Gadhafi that led to this agreement: the pair would be sent for trial in a neutral country under the rules of Scottish law (the Scottish legal system has historically been different from that of England and the rest of the UK). The neutral country agreed was the Netherlands. The two Libyan men were handed over to authorities there in late 1999 and the trial began in February 2000. A year later Megrahi was convicted, his co-defendant found innocent.

But that would never be the end of the story. Megrahi appealed his conviction. The appeal was denied. He then applied for a judicial revue, this was a more successful maneuver. New facts came to light. Exculpatory evidence — a break-in at Heathrow airport the night before Pan Am 103 took off — was withheld from the defense. His lawyers claimed that it was possible the bomb was planted during the break-in. In 2007, Megrahi was granted leave to appeal a second time.

Meanwhile other aspects of the case were resolved. Libya agreed to pay compensation of around $8 million to each family. In return the U.N. removed all sanctions from Libya. Gadhafi began a rapid process of rehabilitating his nation from being a pariah to a key supplier of oil to the west.

In 2007, in one of his final acts as prime minister, Tony Blair went to Libya to meet with Gadhafi and signed a memorandum, a Prisoner Transfer Agreement, at around the same time British Petroleum entered into a long-term multi-billion dollar with the Libyan National Oil company to develop Libya's massive oil reserves.

Other things changed as well. Tony Blair campaigned on a platform of devolving power to Scotland. Following his victory in the 1997 election, Scotland was allowed to form a government with its own parliament. Scottish nationalist politics began to muddy the waters. In June 2007, the Scottish National Party won a majority of seats and formed a government for the first time.

Scotland's First Minister, Alex Salmond is a nationalist and he expressed anger at the time that Blair had in effect committed the Scottish government to transferring Megrahi at some point in the future. Salmond saw that as an infringement of Scottish sovereignty.

Today, MacAskill said the Libyan government had indeed made an application for Megrahi's transfer under the agreement. He rejected that request.

In a final twist of the story, Megrahi dropped his appeal earlier this week. Under Scottish law he could not be released while there were legal proceedings underway. Swire and others had hoped that in the appeal court new evidence would come out that would bring the truth of what happened closer.

So now Megrahi is en route to Libya and there is bitter disappointment for those who sought punishment and those who sought truth. He will die in Libya surrounded by his family and friends. He will take his secrets to the grave with him and the government of Libya will be under no compulsion to make public what it knows.

The only way forward now would be for the British and American governments to tell us what they know — or hold a further public review of events. Justice Minister MacAskill, acknowledged today, "There are questions to be asked and answered about the case but they are beyond the jurisdiction of the Scottish government." He added Scottish authorities would be willing to assist in answering those questions.

But it is unlikely that the American and British governments will ever get around to asking them.