Confessions were an arbitrary concept - in truth, the vast majority of S-21 prisoners were probably innocent of the charges against them, so therefore most prisoners' admissions were lies borne out of excessive torture. Even loyal Khmer Rouge cadres would eventually admit to spying for the CIA or the KGB, secret loyalty to the Vietnamese, sexual crimes - whatever the interrogators asked for they usually got. It was only a matter of time before the torture would break even the strongest of prisoners. The dubious nature of the confessions mattered little to the Khmer Rouge leadership; like the Salem witch trials of puritan Massachusetts, each confession fanned the fires of conspiracy by offering new names (and people) to target. Because prisoners would often name names in their forced confessions, the confessions served as a misguided, but self-fulfilling prophecy to the Khmer Rouge, allowing them to proove to themselves that there was indeed a massive web of traitors amongst them.

Thousands of these confession files, including 5,000 photographs, survive to this day, giving us a grim look at the activities that occured inside Tuol Sleng. The Yale Cambodian Genocide Center has spent many years examining these records, but thousands of the people sent to S-21 have yet to be identified. We may never know who they were or why they were sent there; only their portraits remain to serve as affirmations of their lives - and deaths - at Tuol Sleng

http://www.edwebproject.org/sideshow/khmeryears/s21.html