I think that is honestly the single most disturbing portrayal of a psychopath I have ever seen in fiction, mostly because of his utter nonchalance about his actions. And I've read lots of mystery novels. What is particularly disturbing about him is that you don't see him being a psycho coming. At all. At least I didn't. And it's to the point where I think even mentioning his name as a villain is a pretty big spoiler. Then again I hadn't read nearly as many mysteries when I read Larsson as I have now.