The Democratic Kampuchea period of 1975-1979 saw the closure and destruction of schools, the decimation of the teaching service and the cessation of formal education at the hands of the Khmer Rouge. Phung Ton, the dean of Phnom Penh University, was arrested, tortured and murdered at Tuol Sleng (S-21). During this period Phnom Penh University and all other educational institutions in Cambodia were closed down. Under this regime an education was perceived as a dangerous asset. Hence, the educated were targeted, and most of the university's teachers and students were killed. The campus was abandoned and remained deserted for almost five years. Of the educated people who survived, few remained in Cambodia once the borders reopened following the Vietnamese invasion that toppled Khmer Rouge rule.