The failure of Cambodian troops in the Eastern Zone to successfully resist the Vietnamese incursion made Pol Pot suspicious of their allegiances. He ordered a purge of the Eastern Zone, with over 400 CPK cadres from the area being sent to S-21. Aware that they would be killed on Pol Pot's orders, increasing numbers of Eastern Zone troops began rebelling against the Khmer Rouge government. Pol Pot sent more troops into the Eastern Zone to defeat the rebels, ordering them to slaughter the inhabitants of any villages that were believed to be harbouring any rebel forces. This suppression in the east was, according to Short, "the bloodiest single episode under Pol Pot's rule". Fleeing the government troops, many leading rebels—including Zone deputy chiefs Heng Samrin and Pol Saroeun—made it into Vietnam, where they joined the anti-Pol Pot exile community. By August 1978, Pol Pot could only consider Mok's forces in the south-west and Pauk's in the Central Zone as being reliable.
The failure of Cambodian troops in the Eastern Zone to successfully resist the Vietnamese incursion made Pol Pot suspicious of their allegiances. He ordered a purge of the Eastern Zone with over 400 CPK cadres from the area being sent to S-21. Aware that they would be killed on Pol Pot's orders, increasing numbers of Eastern Zone troops began rebelling against the Khmer Rouge government. Pol Pot sent more troops into the Eastern Zone to defeat the rebels, ordering them to slaughter the inhabitants of any villages that were believed to be harbouring any rebel forces. This suppression in the east was according to Short, "the bloodiest single episode under Pol Pot's rule". Fleeing the government troops, many leading rebels—including Zone deputy chiefs Heng Samrin and Pol Saroeun—made it into Vietnam, where they joined the anti-Pol Pot exile community. By August 1978, Pol Pot could only consider Mok's forces in the south-west and Pauk's in the Central Zone as being reliable.