Since WW2 camps were brought up and I didn't see this one mentioned...
Unit 731. A Japanese biological and chemical warfare research center in WW2, and responsible for some of the worst war crimes committed by Japan. Somewhere between 3,000 and 12,000 men, women and children were experimented on in his one camp alone, and does not include victims from other sites. Experiments done on living victims were: vivisection without anesthesia; removing internal organs to study effects of disease; amputating limbs to study blood loss (some were re-attached to the other side of the body); stomachs being surgically removed and the esophagus attached to the intestines; inducing frostbite and chipping away at the frozen flesh; syphilis experimentation involving injections, rape, and forced pregnancy to study transmission; tests to determine length of time until death including high-pressure chambers, lethal doses of x-rays, injected with animal blood, injected with sea water, chemical tests in gas chambers, placed in centrifuges and spun until death, and burned or buried alive.
No researchers were tried for war crimes and instead given complete immunity in exchange for their data on human experimentation.
The New York Times did an article about this lack of prosecution
here.