Formerly the Tuol Svay Pray High School, named after a royal ancestor of King Norodom Sihanouk, the five buildings of the complex were converted in March or April 1976 into a prison and interrogation center. Before other buildings in town were used already as prison S-21. The Khmer Rouge renamed the complex "Security Prison 21" (S-21) and construction began to adapt the prison to the inmates: the buildings were enclosed in electrified barbed wire, the classrooms converted into tiny prison and torture chambers, and all windows were covered with iron bars and barbed wire to prevent escapes and suicides.