This article was produced in partnership with the Pulitzer Center on Crisis Reporting.

GUANTÁNAMO BAY, Cuba — It was May 2003, a year into the C.I.A. program that had led to three detainees being waterboarded hundreds of times in search of information about possible terror plots, and the agency needed to train more interrogators. At a classified prison in Afghanistan known as the Salt Pit, trainees took turns practicing “insult slaps and attention grabs” on a naked prisoner named Ammar al-Baluchi.