Many of the surviving eastern zone leaders fled into the jungle where they hid from and fought center zone troops. In October 1978, Chea Sim led a group of 300 people across the border into Vietnam, and the Vietnamese then launched a raid into the eastern zone that allowed Heng Samrin and his group of 2,000 to 3,000 soldiers and followers to seek refuge in Vietnam. Meanwhile, the center decided that the entire eastern zone was full of traitors and embarked on a large scale purge of the area, with over 10,000 killed by July 1978, while thousands were evacuated to other zones to prevent them from defecting to the Vietnamese. The center also stepped up purges nationwide, killing cadres and their families, "old people" and eastern zone evacuees who were regarded as having dubious loyalty.