Kaing Kek Ieuv, alias "Duch," the former head of the Khmer Rouge's S-21 (Tuol Sleng) torture and interrogation center, is currently on trial by a UN-backed tribunal in Phnom Penh for crimes against humanity and war crimes. As an insight into how the prison worked, what follows is a chapter from Sara Colm and Sorya Sim's book, Khmer Rouge Purges in the Mondolkiri Highlands, Region 105, soon to be published by the Documentation Center of Cambodia.