The Santebal established over 150 prisons for political opponents; Tuol Sleng is a former high school that was turned into the Santebal headquarters and interrogation center for the highest value political prisoners. Tuol Sleng was operated by the Santebal commander Khang Khek Ieu, more commonly known as Comrade Duch, together with his subordinates Mam Nai and Tang Sin Hean. According to Ben Kiernan, "all but seven of the twenty thousand Tuol Sleng prisoners" were executed. The buildings of Tuol Sleng have been preserved as they were left when the Khmer Rouge were driven out in 1979. Several of the rooms are now lined with thousands of black-and-white photographs of prisoners that were taken by the Khmer Rouge.