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EDINBURGH, Scotland -- Scottish officials said Saturday they were right to release a Libyan man convicted of the Lockerbie bombing because he was dying of cancer, even though he is still alive two years later.

Abdel Baset al-Megrahi was convicted in 2001 of murdering 270 people, most of them American, by blowing up a Pan Am plane over the Scottish town of Lockerbie on Dec. 21, 1988.

He was freed on Aug. 20, 2009, after prison doctors said he had prostate cancer and estimated he had only three months to live.

He is still alive, and last month he appeared at a televised rally in Tripoli alongside Muammar Qaddafi.

In a statement, a spokesman for Scottish First Minister Alex Salmond said the decision to release al-Megrahi was made "on compassionate grounds and compassionate grounds alone" and was not influenced by economic, political or diplomatic factors.

"Whether people support or oppose the decision, it was made following the due process of Scots law, we stand by it, and al-Megrahi is dying of terminal prostate cancer," he said.

A leading cancer specialist, however, said 59-year-old al-Megrahi appeared to be receiving a cutting-edge hormone treatment and could live for several more years.

Prof. Roger Kirby, a consultant urologist at the Prostate Cancer Center in London, said doctors in Scotland would have been unaware of the new hormone-based therapy abiraterone, which was recently approved by the U.S. Food and Drug Administration and is still not available in Europe.

"He has long outlived the speculative three-month prognosis, and it appears he may continue to do so for a while yet," Kirby said. "I strongly suspect that this drug has been central to that."

Al-Megrahi, a former Libyan intelligence officer, is the only person convicted over the Lockerbie bombing, Britain's worst terrorist attack.

His release infuriated the families of many Lockerbie victims, who suspected Britain's ulterior motive was to improve relations with oil-rich Libya. Some relatives, however, believe al-Megrahi was wrongly convicted and that evidence points to Iranian-backed Palestinian militants as the perpetrators.

American politicians and British leaders also have condemned the decision by Scotland's semiautonomous government to free the convicted bomber.

The second anniversary of al-Megrahi's release comes as Libyan rebels gain ground in their six-month civil war against Qaddafi's Tripoli-based regime. Some politicians in Britain and the U.S. have called for al-Megrahi to be re-imprisoned if Qaddafi is overthrown.

George Foulkes, a Labour Party member of Britain's House of Lords, said this week that al-Megrahi should be sent back to Britain by a post-Qaddafi government.

Sen. Robert Menendez of New Jersey, a Democratic member of the U.S. Senate Foreign Relations Committee, has said any new Libyan government should agree to extradite the bomber to the United States.

Guma El-Gamaty, the British organizer for Libya's opposition, said last month any decision on al-Megrahi's future would have to wait for "an elected democratic government in Libya."

Until that time, he said, "we are not in a position to give that commitment."

The British government said it was powerless to intervene.

"Megrahi was convicted in a Scottish court under Scottish law," a Foreign Office spokesman said, on condition of anonymity in line with government policy. "He could be returned under the terms of his release but this is matter for the relevant judicial authorities and it is not something that the British government can interfere with."

Officials in Scotland tasked with overseeing al-Megrahi's parole conditions said they monitored him by regular video link conferences -- and expected to continue to do so.

"We have been with him regularly and recently and he has never breached his parole," said George Barber, a spokesman for East Renfrewshire Council near Glasgow.

"Our contact with him is direct and not through any third party or the Libyan government, so we are operating on the basis that the arrangement will continue regardless of what happens in Libya."