It might be the reason he can't remember killing those students. And how he is able to turn off his conscience and perform the murders etc that he does.

well he doesn't remember he is dead so there is something there

It could be :)

I've heard of a theory involving a twin (Taint) but I believe the split personality thing, that might be why Constance wanted him to see Ben so badly...

I think it could be possible. Did you see when he took off the rubber man suit mask and we discovered it was him? You can see two different looks in his face then, one is confused, like a child, like he doesn't really know what he's doing; and the other one is evil and he smirks, like if everything is going according to his evil plan. :S