Speaking at a memorial service in Westminster Abbey yesterday on the 25th anniversary of the atrocity, Swire, who also announced his intention to stand down as the UK's leading Lockerbie campaigner, described the bombing that killed 270 people, including his 23-year-old daughter Flora, as a "revenge attack".
His comments came as the British, American and Libyan governments pledged to work together to uncover "the full facts" of the bombing.
Megrahi was convicted in January 2001 and was given a life sentence. He was diagnosed with prostate cancer in 2008, leading to a decision to free him under compassionate release rules. He died in Tripoli, Libya in May last year.
Swire said: "Nelson Mandela made forgiveness look easy. But even a truth and reconciliation commission cannot work unless first the truth is known.
"When I first met the late al-Megrahi face to face in Greenock prison, though he was a practising Muslim, he had bought me a Christmas card in the prison shop. In it he had written, 'Dr Swire and family, please pray for me and my family'.
"He died, my friend. Over Christmas, if you pray, please pray for his innocent family but also for all those who wrestle with hatred, that they may be healed by God's love. Please pray also that we who will sit down at a Christmas table with chairs forever empty may find peace."
Swire added: "In our family, Flora was our beautiful, vivacious first-born of three wonderful children. We are the lucky ones, in the UK and USA. Not only do we live in two of the most free and safe countries in the world but we relatives also had the joy of living with those we loved until their untimely deaths."
Yesterday, in a joint statement released for the 25th anniversary, the British, American and Libyan governments said they want "all those responsible for this most brutal act of terrorism brought to justice".
"We are committed to co-operate fully in order to reveal the full facts of the case," the statement added. "We will all provide full support to the investigation team to enable them to complete their inquiries successfully. We are striving to further deepen our co-operation and welcome the visit by UK and US investigators to Libya in the near future to discuss all aspects of that co-operation, including sharing of information and documents and access to witnesses."
Scotland's top law officer, Lord Advocate Frank Mulholland, has also announced that Libya has appointed two prosecutors to work on the investigation into the bombing.
Megrahi's family have said they plan to appeal against his conviction. Megrahi died last year protesting his innocence. Now his family hope the Libyan government can help fund the appeal process. His brother Abdel-Hakim al-Megrahi, said: "We want to appeal and we wish for the truth to be revealed. This is not just for our own benefit but also for the benefit of the families of the victims and for public opinion.
"We need to know who committed this horrible crime. But, as you know, we as a family cannot afford to pay for the appeals process.
"God willing, the Libyan government will do this, but it has to be launched by the family first."
Earlier this week, some of the British relatives of Lockerbie victims said they were considering making another appeal against Megrahi's conviction.
Swire, now 77, also told the Sunday Herald about his plans to step back from leading the British families' campaign for justice.
The retired GP said: "I never thought for a moment that we would be in this position 25 years later. We still don't have the truth. And, unfortunately, I can't campaign to get my daughter back. I've always tried to do what Flora would be proud of, she was a seeker after truth herself.
"But I have got to the point where I really have to cut back on it. It's time to relax and leave it to a younger person. The time has come for someone else to take over."
Swire added: "The 25th anniversary is no more poignant than any other, this is a loss we have to live with every day. Flora will never come back. But what makes this loss even harder is that - 25 years on - we still don't have answers."
He admits that the campaign has been a way of coping with the grief for his daughter.
Swire believes that the case against Megrahi was flawed, and has even referred to Megrahi as the "271st victim": "For 25 years, our calls for an inquiry into why Lockerbie was not prevented have been ignored and blocked at every stage. I believe that, eventually, yes, the Megrahi verdict will be overturned."