Inscription: BUILDING "C". - Ground floor: single cells, made of brick. - First floor: single cells, made of wood. - Second floor: mass detention. The braid of barbed wires prevents the desperate victims from committing suicide.
In 1975 the Khmer Rouge turned Tuol Svay Prey High School into a prison and interrogation center known as Security Prison 21. It became the largest detention center in the country, and out of almost 20,000 prisoners detained there only seven survived. When the Vietnamese liberated Phnom Penh in 1979, they turned the prison into a genocide museum. Building C consists of 2 stories, ground floor was used as single brick cells, the first floor was used as single wooden cells and second floor was used as a mass detention.