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 due to the US government both classifying incriminating evidence, as well as blocking the prosecution access to key witnesses.
During the occupation, MacArthur assigned Lieutenant Colonel Murray Sanders to gather data on Japan's biological warfare, which was obtained through human experimentation.
At Sanders' suggestion, MacArthur offered full political immunity to high-ranking officials who were instrumental in perpetrating crimes against humanity, in exchange for the data about their experiments.
Though it is unclear on whether Emperor Hirohito was made aware of the full extent of Unit 731, the emperor's younger brother, Prince Mikasa, had toured the headquarters of Unit 731 and wrote in his memoirs that he watched films of how Chinese prisoners were "made to march on the plains of Manchuria for poison gas experiments on humans.
"[8] MacArthur, abiding by the Potsdam Declaration, gathered a jury for the Tokyo trials, where a number of Japanese officials were successfully tried and convicted.