I think he must've had a moral conscious at some point in his life, because I don't believe it's physically possible to be born without one, even if you have a child that has known abuse since day one, they must realize that that is not how humans are supposed to treat other humans.

I think that maybe he somehow lost his conscious through neglegance (did I spell that right?), like, he ignored it so much in the begining that it just kind of...died.

Or maybe, his conscious was there the entire time, but he satisfied it by truly believing the things he did weren't wrong? Like, you can't feel bad about something if you think you were justified in the act, so he could've honestly believed that what he was doing was completely justifyable and right, then his conscious wouldn't have bothered him at all.

Sorry if that was confusing, I get a litte carried away with this phycological analogy things...