American cover-up of Japanese war crimes

The 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.
Cover-up.
The American government sent General MacArthur to oversee rebuilding post-war Japan and the shift to a democracy from a previously feudalist system of governance. MacArthur was also responsible for gathering data on biological warfare, which was obtained through human experimentation. The US government offered full political immunity to high-ranking officials who were instrumental in perpetuating crimes against humanity, in exchange of the data about their experiments. Among those was Shiro Ishii, the commander of Unit 731. During the cover-up operation, the U.S. government paid money to obtain data on human experiments conducted in China, according to two declassified U.S. government documents.
The total amount paid to unnamed former members of the infamous unit was somewhere between 150,000 yen to 200,000 yen. An amount of 200,000 yen at that time is the equivalent of 20 million yen to 40 million yen today. 
Hirohito, as emperor, gave his consent regarding the policies and activities of Unit 731, Unit 100 and other human experimentation facilities. Although there is no evidence that he was thoroughly informed on most of the atrocities that occurred within the facilities. He was one of many that would be granted immunity. MacArthur, abiding by the Potsdam Declaration, gathered a jury for the Tokyo trials, where a number of Japanese officials were successfully tried and convicted.