Unidentified Cambodian prisoner at S-21 in Phnom Penh. This is one of 7,000 remaining photographs from the prison, and this negative was damaged from years of neglect. One former prison guard described a concerted effort to destroy both written and photographic records prior to the Vietnamese invasion in December 1978 that ended the Khmer Rouge's brutal four years in power. Photo: © Tuol Sleng Museum of Genocide