I have mixed feelings about this. On the one hand, he is a mass murderer and properly must remain in prison for his life.
However, he has less than three months to live, so he has remained in prison practically all his life. Besides, he was not the instigator of the bombing, he was probably just a pawn, carrying out the orders from higher up (perhaps even from Khaddafi himself).
Plus there is something in what the Scottish minister said. We have certain standards, certain principles we live by, and compassion, justice tempered by mercy is one of them. If we sink to their standards, their level, it makes us no better than the terrorists.
But the crime was so horrible, so heinous that one has to question whether normal standards of compassion, mercy should apply. So I can see arguments on both sides.