In September of 1943, the United States began its own research on biological weapons, even after President Roosevelt made a statement warning Japan to stop using poison gas in its war on China. Lt. Col. Murray Sanders led the program at Camp Detrick in Maryland.
"After the war, the Allies discovered the existence of Japan's Unit 731, a special military unit that experimented on prisoners of war to develop biological weapons. Ironically, the U.S. was secretly developing its own biological warfare program with Roosevelt's full knowledge and approval at the time of his warning to Japan. Japan continued its use of these weapons, but on a smaller scale, until the end of the war, managing to keep its activities secret."
~This Day in History: June 5, 1942
Sanders was the first U.S. investigator of Unit 731. Sanders interviewed many notable military leaders and scientists of Unit 731, although he never spoke to Ishii. Sanders' translator was Ryoichi Naito, an English speaking Japanese officer. Throughout Sanders' time investigating the unit, Naito was able to mislead him into believing the Japanese did not have anything to do with the experiments. The US government soon found proof. They also discovered that Naito was in fact very close to General Ishii.
In 1945, towards the end of the Pacific War, general Shiro Ishii ordered for Unit 731 to be blown up, destroying any evidence of the atrocities committed. He faked his own death, hoping to escape his punishment. However, when the United States discovered he was still alive, they forced the Japanese to hand him over. At first, Ishii denied that he ever had anything to do with the unit. However, knowing that the Soviets also wanted to "speak" with him, Ishii offered to give the United States all of the information obtained through the experiments in exchange for immunity. The United States agreed.