Mas'ud, who has denied building and priming the bomb that brought down Pan Am Flight 103 over Lockerbie on 21 December 1988, killing 270 people, is asking a judge to throw the case out of court on the grounds of unlawful rendition.
In a filing made public this week, his legal team detailed what they describe as a "cloak and dagger operation conducted in the dead of night," in which armed men seized him from Libya and transferred him to FBI agents with a plane waiting to fly him out of the country.
The US government charged Mas'ud with destroying the airliner in December 2020. His trial, which has been postponed three times, is currently scheduled to begin in January.
The Department of Justice has argued that, under US law, the method of his removal from Libya should not prevent the case from proceeding.