Why did the Japanese deny (and continue) to deny Unit 731's WWII horrors?

Unit 731 (http://en.wikipedia.org/wiki/Unit_731) was Japan's version of German Aushwitz. Biological experimentation on the chinese civilian and live autopsies of the d chinese women are alleged to have been commited along with or autopsy of dutch and American prisioners of war. Why did the America strike a deal with Japan upon entery to not prosecute the offenders? Why did some of the mad scientists of the Japan returned home toa hero's welcome instead of a well deserved death? How come Japan still refuses to accept the horrors of its past and make peace with them? More surprisingly what was the cause of the American cooperation with the japanese to conceal the evidence? Did America want to benefit from the scientific data? This topic is limited on the net. Please give me your answers, insight, or pointers if you are knowledgable. Sources would be appreciated. I am very curious for the sake of truth at least.