Roughly 1.7 million people died in Cambodia from untreated disease, starvation, and execution during the Khmer Rouge reign of less than four years in the late 1970s. The regime's brutality has come to be symbolized by the multitude of black-and-white mug shots of prisoners taken at the notorious Tuol Sleng prison, where thousands of "enemies of the state" were tortured before being sent to the Killing Fields. In Archiving the Unspeakable, Michelle...