American cover-up of Japanese war crimes occurred after the end of World War II , when the occupying US government granted political immunity to military personnel who had engaged in human experimentation and other crimes against humanity , predominantly in mainland China . The pardon of Japanese war criminals , among whom were Unit 731 's commanding officers General Shiro Ishii and General Masaji Kitano , was overseen by General of the Army Douglas MacArthur in September 1945 . While a series of war tribunals and trials was organized , many of the high-ranking officials and doctors who devised and respectively performed the experiments were pardoned and never brought to justice . As many as 12,000 people , most of them Chinese , died in Unit 731 alone and many more died in other facilities , such as Unit 100 and in field experiments throughout Manchuria
Unit 731
Unit 731
American cover-up of Japanese war crimes