the US struck a secret agreement with Ishii. In a memo to General Douglas MacArthur (1880 – 1964), commander of Allied forces in Japan, Washington recognized that although war crimes had been committed, the experiments led by Ishii and his colleagues were “almost incalculable and incredibly valuable to the United States.”
In exchange for the records of Unit 731’s experiments, the US granted Ishii and his assistants immunity. Ishii died, and his collaborators went on to have careers in prestigious universities and private laboratories.
Ishii Shiro is a prime example.
He was the head of Unit 731 and did things like live and unanesthetized vivisections on people, bioloogical weapons testing on children, etc… Which is among the milder things. The US made a deal for all his data, and he lived his last years in peace and anonymity as a free man. He actually worked for free as a local doctor for a period.
If you look up information about him in Japanese sources, most of it is apparently all about how was such a nice man who helped people, and basically that he did a little oopsie in the 40s.
That’s one of the worse parts, they didn’t really gain any of the knowledge they hoped for:
https://en.wikipedia.org/wiki/Unit_731
From what I’ve gathered, the experiments of unit 731 were more like shengele, more focussed on cruelly than actual science
Not to mention there was often no method or recorded data, so even calling them “science” of any kind is doubious.
At least he repaid some of his debt to society.