"As of today, Unit 731 is arguably one of the most thoroughly researched and best documented among many known episodes of Japanese war crimes. It may be also said that the highly organized and institutionalized nature of Unit 731’s criminality likely made it comparatively easy for researchers to develop a comprehensive picture of Unit 731’s wartime activities once relevant oral and documentary histories became available. To achieve the same level of comprehensiveness would be challenging with other episodes of large-scale Japanese war crimes, such as the Nanjing Massacre, whose occurrence could not be attributed to the establishment and operation of a single Unit 731-like criminal organization. In a word, the crimes committed by the members of Unit 731 were a case of “criminality of closed systems” in the sense that the unit members made systematic use of humans for medical experimentation in fulfillment of their specific organizational mission, just like the members of concentration camps in German-controlled Europe gassed to death the Jewish people in fulfillment of the camps’ organizational mission."