I completely agree with you. Especially about the compartmentalizing of both the crime and perhaps the impulses that compelled him to do this. If I were to hazard a guess, I think he was driven by a compulsion to commit this crime, and that there will be no real motive like robbery etc...In addition, I wonder if some of the pictures and comments traded with some of the girls were also not a way of testing to see if those close to him would ever suspect such a thing of him while also releasing some of his secret in an abstract way.
I feel for those close to this young man, he obviously was full of talent and had a bright future. However, after looking at his MySpace, and especially those interactions with the girls on there, I got the distinct possibility that he might have some deeper issues. Of course, like somebody mentioned earlier, I'm forming my theory after the fact, so I could be looking for things to reinforce a theory. Irregardless, if he did this, he needs to be locked up.