Amnesty International’s deputy regional director for the Middle East and North Africa, Diana Eltahawy, said they have long called for accountability for crimes [including the Lockerbie attack] under international law but this has to be done in a manner that respects due process and upholds fair trial rights.

"In this case even a facade of legality was not maintained … there was no hearing for [Masud] to challenge the lawfulness of his detention and transfer.” Eltahawy told The Guardian.

Eltahawy also said that relying on “commanders of abusive militias and armed groups … for law enforcement or special operations only further entrenches their power and emboldens them to commit further horrific crimes”. While Jake Sullivan, the US national security adviser, said last week that Masud had been brought to the US “in a lawful manner according to established procedures”.