@Mayumien I mean he is obviously trying to seduce her. Also, he said he didn't take interest for Lucy because she was still too young. The women he killed before probably were all tired of their life and needed an outlet. He probably got some Oedipus' issue and "needs" women until they don't fell in love with him, at that point they are "easy" and "impure" so he rid of them. He targeted Isabella because she saw him after he killed Rachel.