"Something terrible happened here. And I don't know what it is," Bill Herod remembers thinking in his first days in Phnom Penh in 1980. He was with Church World Service, one of a group of aid workers allowed into the country after the Vietnamese overthrew the Khmer Rouge in January 1979 and put an end to the three-and-a-half-year-long nightmare of the Cambodian people. In 1980, Herod had just come from Vietnam. He had seen plenty of devastation, but this was something different, a higher order of magnitude.