Toul Sleng Museum used to be a high school, but was turned into a prison by Pol Pot's security forces in 1975. It was called Security Prison (S-21) and became the largest detention and torture center in Cambodia. For the next three years over 17,000 individuals were held here and later taken to Choeung Ek (Killing Fields). I decided not to visit the later. Prisoners who were killed during torture were buried in mass graves on the prison grounds. There have been comparisions made between the Nazis and the Khmer Rouge with their precise record keeping during the inhuman treatment of prisoners. Pictures were taken before and after treatment. There were also some foreigners held here before being murdered. Above are various signs that explain the museum and the security measures that were enforced.