One of my co-workers is originally from Cambodia, and he told me one time that most of his extended family died in the Cambodian killing fields. He was very young at the time, but he remembered seeing men in uniforms walking down his street and knocking on doors. His mother scooped him up and ran out their back door before the soldiers reached the house. They hid in a small shack until the soldiers and the other people left in trucks.
He said life under Pol Pot was always terrible, but he didn't know anything about the Khmer Rouge or the killing fields until his mother got them both to a refugee camp on the Vietnamese border. He found out much later that all of the people he saw being driven out of town that day were taken out to a swamp and shot to death. He was lucky to survive.