IT was just a single day in Phnom Penh, one of many, but even now I can’t get it out of my head. The genocide was over — Vietnam, the traditional enemy, had ended it by driving out the Khmer Rouge and setting up a collaborationist government. But in 1988, Cambodia was still mourning. So many people had died, and thousands of refugees, including those who had suffered from the Khmer Rouge and those loyal to it, lived in politicized border camps inside Thailand, waiting for a diplomatic settlement that never quite seemed to arrive.