In Flags of our Fathers James Bradley recounts how he had invited his parents to visit Japan when he was studying there in the 70's (I think it was the 70's). He father, a corpsman on Iwo Jima made famous by the Joe Rosenthal photo, refused because of the memory of what they had done to one of his friends on the island. The Germans may have killed POW's but the Japanese seem to delight in torture and prolonged mistreatment of allies. (Perhaps that more resembles the German's approach to Russian POW's.)
Here is the Article about Unit 731 I told you about. It not only goes into what they did but discusses, in depth, our complicity after the fact. As with the Germans we used for spying and technological advancement, we used the Japanese for their research we couldn't do ourselves. And while we let these sadists go free, we didn't net much their "research." It was all for naught.