As part of their basic training, American soldiers are sent on a course that simulates being captured by the enemy, where they are taught how to withstand abusive interrogations. When the CIA started rounding up suspected members of al-Qaeda in Afghanistan in 2002, it called in two former instructors from the course to give them advice.

Reverse-engineering their insights on surviving torture, the two men recommended to the CIA a series of interrogation methods that included mock burials, standing in stress positions for long periods of time and the now infamous “waterboarding” to mimic drowning.

Over the course of the next six years, the two retired Air Force psychologists became the central figures in a CIA programme that detained more than 100 suspects in secret prisons around the world, subjected many of them to torture and opened up the biggest crisis at the agency in a generation.