"It's all quite simple. I don't want to die."

It really is that simple. How he keeps from dying, the method, that's where it gets complicated but the motivation is rather simple. That is what separates him from other killers. Serial killers are often broken in some way while Joseph likes to consider himself quite the opposite of that. There is nothing more natural than wanting to live.

She was bound now, arms restrained behind her back and feet bound at her ankles. There was nowhere she could go at the moment anyway.