The researchers involved in Unit 731 were secretly given immunity by the United States in exchange for the data they gathered through human experimentation. Other researchers that the Soviet forces managed to arrest first were tried at the Khabarovsk War Crime Trials in 1949. The Americans did not try the researchers so that the information and experience gained in bio-weapons could be co-opted into their biological warfare program, much as they had done with German researchers in Operation Paperclip. On 6 May 1947, Douglas MacArthur, as Supreme Commander of the Allied Forces, wrote to Washington that "additional data, possibly some statements from Ishii, can probably be obtained by informing Japanese involved that information will be retained in intelligence channels and will not be employed as war crimes evidence". Victim accounts were then largely ignored or dismissed in the West as communist propaganda.