They keep making comparisons to Buffalo Bill in the film The Silence of the Lambs, a fictional guy who was diagnosed as transgender but couldn't get the surgeries he wanted so he abducted women and tortured them into slathering lotion on themselves all day to soften up their skin, in preparation to kill them and make a skinsuit out of female human leather.
Just from the sound of it, the killer in this novel is a transtrender dude who pretends to be a woman so they'll be less wary of him, making them easier to prey on. Not sure how that'll be developed. It goes with JK Rowling being very untrusting of men in general, from what I've seen of her behavior.