Do you think perhaps it was because he knew about the pregnancy? In Alone when Sculptham was naked infront of her mirror he looked her over (saw her body-- baby bump?) and stared at her in disgust, I'm thinking it was more then just her finding him 'exciting' and was sexually excited by him. Aswell as perhaps an inner disgust with herself, but it could have foreshadowed that he knew and he didn't like the idea of being a father.
It's unsure really, being a soft-spoke paedophile slash rapist it's really hard to tell. He obviously made good friends with his inmate during his time in prison.
Maybe the idea of his victims (I do believe in Alone the newspaper clipping said something about women-- not just Scultpham, not reporting due to the idea of it being exciting? Could be wrong, I know Sculptham left her door unlocked.) enjoying the rape it became unpleasurable. He could have just went insane too.
What's that then Albert Vaginastein ?
R.I.P Moral Orel 2005-2008.