Former Scottish justice secretary Kenny MacAskill said he had “always believed” a Libyan national, who will go on trial in the US next year, is the Lockerbie bomber.
The terror act on 21 December 1988 claimed the lives of all 259 people on board Pan Am flight 103 and 11 residents in the Dumfries and Galloway town.
Abu Agila Masud, who is alleged to have helped make the bomb, is due to go on trial in Washington in May facing three charges, which he denies.
In 2001, former Libyan intelligence officer Abdelbaset al-Megrahi was convicted of the murders of 270 people by the introduction of an explosive device onto a civilian aircraft.
But prosecutors maintained he acted with others in carrying out the attack.
MacAskill controversially released Megrahi on compassionate grounds in 2009 after he was diagnosed with terminal cancer.
The US announced charges against Masud in 2020 and he has now been in custody for two years.
Speaking on Radio’s Good Morning Scotland programme, MacAskill said: “I have always believed he is the bomber.”
On the 36th anniversary of the attack, the acting Alba leader said Mr Masud had “what you might call military skills”.
MacAskill added: “He has returned and will face trial in America, I believe he will be convicted, and he is the bomber.”
He added: “Megrahi himself didn’t have the skills to do so, but that doesn’t mean Megrahi didn’t have a role in the operation.”
MacAskill also defended his decision to free Megrahi, who had prostrate cancer, in August 2009.
He returned to Libya but lived until May 2012.
MacAskill said: “We do have rules for compassionate release which exist in Scotland.
“It is dealt with by medical experts. The report came in that he had a prognosis of three months. It was on that basis I released him.
“He was no threat to Scotland, he was a sick man, he lived considerably longer than the prognosis but I think there is reasons for that.”
McAskill, who was SNP justice secretary from 2007 to 2014, added: “I followed the values and laws we uphold in Scotland and sent him home to see out the rest of his life.”
Meanwhile, Scotland’s most senior law officer hopes the forthcoming trial will renew public confidence in the justice process.
Lord Advocate Dorothy Bain KC described the atrocity as “the darkest of days”.
But she believes the US trial of Mr Masud will enable the circumstances of what happened to be “fully understood”.
Ms Bain said: “The bombing of Pan Am 103 over Lockerbie was the darkest of days but the dignity of the hundreds of families so dreadfully affected has always shone as a point of light guiding the pursuit of justice.
“Scotland’s prosecutors and police, working with counterparts in the United States have remained steadfast in our commitment to uncovering the truth and holding those responsible accountable.”
Ms Bain said the original trial at the Scottish Court in the Netherlands considered Crown evidence from 227 witnesses over 72 days before Megrahi was convicted.
That decision has been upheld twice at appeal, she added.
The Lord Advocate said: “Despite this long-running and intense scrutiny, I am aware that not everyone shares the same view of the Crown case.
“I have always believed in the power of the legal process as a tool for fairness and public trust.
“The forthcoming trial in Washington will bring the facts of this case before the public again, and the circumstances of what happened can be fully understood.”
Scottish Secretary Ian Murray said the anniversary was a time for reflection.
He added: “Our thoughts are with the families and friends of the 270 who perished in the air and on the ground, and all those in the town who saw such devastation rain down on them.”
Public interest in Lockerbie will also be rekindled next year by two television dramas and a play.
A new drama, Lockerbie: A Search For Truth, starring Oscar winner Colin Firth, is due to air on Sky Atlantic on January 2.
It will be followed later in the year by a six-part series.
And in the autumn a new stage production about the town of Lockerbie’s response to the Pan Am disaster is to reopen the Citizens Theatre in Glasgow.
Earlier this month, Scotland’s prosecution service said parts of the wreckage of the downed plane were being transferred to the US as evidence ahead of the trial.
The Boeing 747 plane exploded above Lockerbie, 40 minutes into its flight from London to New York.
Megrahi is the only man convicted in relation to the bombing, after being found guilty of 270 counts of murder by a panel of three Scottish judges, sitting at a special court in the Hague in 2001.