 At these locations, the Kwantung Army was also responsible for some of the most infamous Japanese war crimes, including the operation of several human experimentation programs using live Chinese, American and Russian civilians, and POWs, directed by Dr. Shiro Ishii.Arrested by the American occupation authorities, Ishii and the 20,000 members of Unit 731 received immunity from prosecution of war-crimes before the Tokyo tribunal of 1948, in exchange for germ warfare data based on human experimentation.On May 6, 1947, General Douglas MacArthur wrote to Washington that "additional data, possibly some statements from Ishii probably can be obtained by informing Japanese involved that information will be retained in intelligence channels and will not be employed as 'War Crimes' evidence".