in Siem Reap destroyed a munitions depot. Pol Pot suspected senior military figures were behind the bombing and, although unable to prove who was responsible, had several army officers arrested. In September 1976, various party members were arrested and accused of conspiring with Vietnam to overthrow Pol Pot's government. Over the coming months the numbers arrested grew. The government invented claims of assassination attempts against its leading members to justify this internal crack-down within the CPK itself. These party members were accused of being spies for either the CIA, the Soviet KGB, or the Vietnamese. They were encouraged to confess to the accusations, often after torture or the threat of torture, with these confessions then being read out at party meetings. As well as occurring in the area around Phnom Penh, trusted party cadres were sent into the country's zones to initiate further purges among the party membership there. The Khmer Rouge converted a disused secondary school in Phnom Penh's Tuol Sleng region into a security prison, S-21. It was placed under the responsibility of the defence minister, Son Sen. The numbers sent to S-21 grew steadily as the CPK purge proceeded. In the first half of 1976, about 400 people were sent there; in the second half of the year that number was nearer to 1000. By the spring of 1977, 1000 people were being sent there each month. Between 15,000 and 20,000 people would be killed at S-21 during the Khmer Rouge period. About a dozen of them were Westerners. Pol Pot never personally visited S-21. From late 1976 onward, and especially in the middle of 1977, the levels of violence increased across Democratic Kampuchea, particularly at the village level. In rural areas, most of the killings were perpetrated by young cadres who were enforcing what they believed to be the government's will. Across the country, peasant cadres tortured and killed members of their communities whom they disliked. Many cadres ate the livers of their victims and tore unborn foetuses from their mothers for use as kun krak talismans. The CPK Central Command was aware of such practices but did nothing to stop them. By 1977, the growing violence, coupled with poor food, was generating disillusionment even within the Khmer Rouge's core support base. Growing numbers of Cambodians attempted to flee into Thailand and Vietnam. In the autumn of 1977, Pol Pot declared the purges at an end.