Khmer Rouge interrogators at the Tuol Sleng prison in Phnom Penh, Cambodia frequently tortured prisoners by suspending them upside down from these gallows and submersing their heads in the large water jugs underneath. An estimated 17,000 political prisoners passed through Tuol Sleng under the Khmer Rouge from 1975-1979. All but a handful were murdered after months of brutal interrogation. The graves behind the gallows are of 21 unidentified prisoners who were found murdered in their cells when Vietnamese troops entered Phnom Penh and ousted the Khmer Rouge in 1979. March 1, 2012.