Judging by whatever wiki has, the case against Megrahi is not quite open-and-shut. He himself never confessed, and some key witnesses on whom the Scottish judges relied confessed to lying to the court or were alleged to have been paid off/dodgy. Moreover, his alleged partner in the plot was found not guilty, despite the many years of gathering of evidence. Megrahi was appealing at the time of his release, so there may have been fear that the appeal would be successful.

He may as well have been the plotter, but that’s why I’m against death penalty. There are doubts.