As head of Japan's infamous Unit 731 (a covert biological and chemical warfare research and development unit of the Imperial Japanese Army during World War II), Dr. Shiro Ishii (head of medicine) carried out violent human experimentation of tens of thousands during the Second Sino-Japenses War and World War II.
Ishii was responsible for testing vivisection techniques without any anesthesia on human prisoners. For the uninitiated, vivisection is the act of conducting experimental surgery on living creatures (with central nervousness) and examining their insides for scientific purposes.
So basically, he was giving unnecessary surgery to prisoners by opening them all the way up, keeping them alive and not using any anesthetic.
For a disturbing video about vivisection, please go here
During these experiments he would also force pregnant women to abort their babies. He also played God by subjecting his prisoners to change in physiological conditions and inducing strokes, heart attacks, frost bite, and hypothermia. Ishii considered these subjects "logs".
Following imminent defeat in 1945, Japan blew up the Unity 731 complex and Ishii ordered all the remaining "logs" to be executed. Not soon after, Ishii was arrested. And then, the respected General Douglas McArthur allegedly struck a deal with Ishii. If the U.S. granted Ishii immunity from his crimes, he must exchange all germ warfare data based on human experimentation.
So Ishii got away with his crimes because the US became interested in the results of his research.
While not directly responsible for these acts, the actions of the American government certainly illustrated it was more than willing to condone human torture for advancements in biological warfare that could kill even more people.
Not a surprise, considering its past resume. Ishii remained alive until 1959, performing research into bio-weaponry and probably thinking up more plans to annihilate people in different, Dr. Giggles-esque ways to his dying day.