The Tuol Sleng Genocide Museum in Phnom Penh, Cambodia, is a memorial site located on the grounds of former Security Prison 21, also known as S-21. Originally a secondary school called Tuol Svay Prey, the Khmer Rouge regime transformed the complex into a secret interrogation and detention facility between 1975 and 1979.
At that time, the Khmer Rouge imprisoned an estimated 15,000 to 20,000 individuals inside S-21. Detainees were subjected to brutal torture and forced to confess to fabricated crimes against the organization known as Angkar. Once confessions were extracted, prisoners were routinely taken to nearby killing fields such as Choeung Ek for execution.
Only a handful of prisoners survived the prison, usually spared because they possessed specific technical or artistic skills. Following the fall of the regime in January 1979, the abandoned prison was quickly converted into a museum.
History of S-21 Prison
Under the leadership of Pol Pot, the Khmer Rouge regime sought to transform Cambodia into a radical, agrarian society. S-21 operated under the direct supervision of Kaing Guek Eav, known as Duch, who reported to senior party leaders like Son Sen. The prison system aimed to systematically identify and eliminate perceived internal threats and traitors within the population.
Life inside the facility was characterized by extreme cruelty, starvation rations, and strict regulations enforcing total obedience. Detainees were kept in communal rooms or isolated individual cells, chained to iron bars and manacled to floor frames. Interrogations took place multiple times a day using physical beatings, waterboarding, electrocution, and other methods of torture.
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Survivors like painter Vann Nath and mechanic Chum Mei survived because their skills were useful to prison authorities. Vann Nath was assigned to paint portraits of Pol Pot, while Chum Mei was put to work repairing machinery and vehicles. Most other inmates, including women and children, were killed after their interrogations ended.
Documentation and Archival Evidence
The Khmer Rouge maintained an extensive bureaucratic system to record every aspect of the prison's operations. Prison staff logged daily arrest forms, population statistics, execution lists, and detailed interrogation manuals. Inmates were forced to write out long autobiographical confessions multiple times until they matched party expectations.
Every prisoner who entered S-21 was photographed upon arrival by prison personnel like teenager Nhem Ein. Over 6,000 photo negatives, thousands of biographic dossiers, and 4,186 confession files survived the regime's collapse. These photographs and documents were displayed inside the museum classrooms to serve as permanent visual records of the victims.
In 2009, the archives of the Tuol Sleng Genocide Museum were formally inscribed on UNESCO's Memory of the World Register. The archives provide irrefutable documentary proof of state-sponsored terror and centralized planning by the regime. Researchers and legal teams later used these records during international tribunal trials to hold former leaders accountable.
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In the decades following the genocide, the museum has transitioned from a local memorial into an international educational site. Local organizations, such as the Documentation Center of Cambodia, worked extensively to map prisons and mass grave sites across the nation. The site now receives hundreds of daily visitors who come to learn about the history of the Khmer Rouge period.
In July 2025, UNESCO designated the Cambodian Memorial Sites as a World Heritage Site. This inscription includes Tuol Sleng alongside the former M-13 prison and the Choeung Ek Genocidal Center. The official designation recognizes these locations under Criterion (vi) as essential places for reflection, peace, and historical understanding.
