This Article examines two recent decisions of the Pre-Trial Chamber of the Extraordinary Chambers in the Courts of Cambodia (ECCC) in the broader context of whether it is fair to impose criminal liability on Khmer Rouge leaders for acts committed between 1975 and 1979. Since international criminal law was not as fully developed in the 1970s, some of the accused Khmer Rouge leaders argue that the principle of legality ('nullem crimen sine lege") bars many of the charges brought against them. In particular, they have argued that superior responsibility-a mode of liability that holds superiors responsible for the criminal acts of their subordinates had not crystallized into a norm of customary international law by the 1970s.