Former British Foreign Secretary David Miliband said today that releasing the Lockerbie bomber was "clearly wrong".
The Labour leadership contender cast doubt on the medical grounds which allowed the compassionate release of Abdelbaset Ali Mohmed al Megrahi last year.
Megrahi, who is terminally ill with cancer, was given a three-month prognosis and sent home to Libya, sparking anger around the world.
Mr Miliband, who had previously refused to comment either way, told the Herald newspaper today: "It was clearly wrong because it was done on the basis he had less than three months to live and it's now 11 months on."
Megrahi is the only man to have been convicted of the Lockerbie atrocity, which killed 270 people in the bombing of Pan Am Flight 103 on December 21, 1988.
Scottish Justice Secretary Kenny MacAskill authorised his release from Greenock Prison after seeking medical advice, a decision that was met with anger particularly among victims' relatives and politicians in the US.
Mr Miliband continued: "The decision was made in accordance with our constitution and so it was a decision for the Scottish Minister to make.
"Megrahi was released on compassionate grounds and, as I understand it, that depends on him having less than three months to live, so something has gone badly wrong."
The comments come amid further criticism of the way the release was handled.
Prime Minister David Cameron - who is visiting US President Barack Obama - said it was a "very bad decision".
Last week four US Democrat senators called for an inquiry to examine claims that oil giant BP lobbied for his release to smooth an exploration deal with Libya.
And Foreign Secretary William Hague said there was "no evidence" to support the claims.
The UK's representative in Washington has also revealed that the UK Government believes the release of the Lockerbie bomber was a "mistake".
Mr MacAskill has said he would be prepared to assist any inquiry held into the circumstances surrounding the Lockerbie bombing.
The Scottish Government had been asked to consider two applications last year - one for compassionate release on medical grounds and one through a prisoner transfer agreement.
The transfer application, which was rejected by Mr MacAskill, had been made possible by a controversial "deal in the desert" between former prime minister Tony Blair and the Libyan government in 2007.
That deal attracted accusations that it was intended to smooth the way for oil exploration in Libya.
Scotland's First Minister, Alex Salmond, said earlier this week that the US Senate should call Mr Blair to give evidence and "get the truth" about the agreement.
A spokesman for Mr MacAskill said today: "It was David Miliband's own government which did the 'deal in the desert', and David Miliband was foreign secretary when the UK signed the Prisoner Transfer Agreement with Libya - with the clear intention of sending Megrahi back to Libya.
"It was tawdry, and Kenny MacAskill rightly rejected the PTA application. This ludicrous about-turn by David Miliband will damage his credibility and do him absolutely no good, either in his party or anywhere else."