A couple of things people mentioned earlier, about the makeup of an individual such as this might be.
I would speculate that he might certainly be a paedophile, however that doesn't necessarily make them prone to do criminal activity such as rape and murder, but of course it makes them more likely to engage in other illegal activity, such as those online, and because of the stigma and the societal pressure of being attracted to children, they hide it which is probably quite a hard thing to come to terms with.
Being abused as a child, could be a contributing factor, other studies suggest that a paedophile's brain is wired differently to the rest of us, with a link between having more white matter than regular folks, it has also been suggested that it happens to people with somewhat lower IQs on average, and also a link with the length of certain digits in the hand, the index and ring finger, not sure if that is the length compared to each digit?, it's only what I've read, you can probably research it yourselves.
I would say it's easier to classify it as a mental health condition. My own views are quite strong however on this because children are innocent, there are many crimes some which are mind blowing even when adults are just involved. But to me children are no go area... which is why I don't have much sympathy for those who are like that.
I think it comes down to the psychology of the individual and how they see themselves, I can only imagine it must be like an extreme version of guilt, having done the sexual element of the crime, I would imagine they want to hide that crime from others but feel so disgusted with themselves, that in their mind the act of killing the child would diminish the sexual act and in way because they know it is them that is different, some kind of twisted way... to spare the child of having to grow up knowing they've been abused.
I'm not sure if a child killer would have the emotional responsibility / maturity to kill in order to diminish the sexual element of the crime, or wether or not that would make them a psychopath as well as a paedophile by just wanting to brazenly get away with it, which would obviously be a dangerous combo, in any case, either way ...acting on fantasies is obviously a line that should never be crossed.
