It was in 1975, after the victorious entry of the Khmer Rouge troops into Phnom Penh, when the Pol Pot security forces took over the Tuol Svay Prey institute. This institute, one of the most prestigious in the city, located in the heart of the Cambodian capital, was converted into a prison. A corrugated iron double wall, electrified fences, windows with iron bars and classrooms transformed into cells of an extermination prison made up this torture center called Security Prison 21.