Actually, most people are simply incapable of consciously killing another human, regardless of circumstances. In most cases, it takes about six months of brutal conditioning to change that in a military boot camp. And even then, half of it is convincing a recruit that the enemy isn't human. To be able to kill and rape "just like that", one must be dehumanized, as those things go against everything the civilized society conditions us not to do. It's impossible to operate in a human society while completely rejecting this conditioning.
While large-scale wars and prison camps can do this to anyone (indeed, the latter were often designed to do just that), some "people" are like that even without them. The difference is that while someone dehumanized by a war or a concentration camp can remember the life before it and, with some help, regain his humanity, I don't think there's any hope for those who are like that from the beginning.
And as I said before, as a monster, it should be locked down or shot. Exhibiting is another matter, and unnecessary in that case, is it really isn't much to look at.