I think it is interesting that Columbine happened two days before the shooter's seventh birthday; he was then the same age as his victims were to be when shot, I don't know, maybe even attending class in the same rooms where he would murder ( I don't know what elementary school he went to). I think what happened--MOO--is that the perp was the sort of person who (at least when he has no better options or prospects) likes getting violent control over children with violence, torture, sexual assault, forcible sodomy, etc. Probably, I figure, in the first grade he spent much time fantasizing about using violence and torture on his fellow students, but he didn't really understand his controlling tendencies as being for control rather than (say) senseless murder. When Columbine happened, it caused him from imitation to interpret his nasty taste for torture and the other things rapacious males tend to ultimately want as a desire to slaughter children as in Columbine. Maybe Adam Lanza was withdrawn from an early age because he liked to fantasize about doing truly violent heinous things to his fellow classmates or similarly aged children? Perhaps it is normal for people fantasizing or planning the killing of children to not want to be around people much, just from the practical standpoint that if you are thinking about killing people, being around people might cause the sensitive of those around you to get a clue what you are about, contrary to your evil plans.
How exactly would psychologists or psychiatrists discriminate between a person who is withdrawn because he is, I don't know, naturally insanely shy or whatever they say is the cause, and a person who is withdrawn because he is a monster that feels he needs to remain in the dark to hide his monstrousness? I don't think they could, and nor do I think they do. Also, if he really did think of himself as a future child killer from a young age, I can imagine AL often might have made himself look weird in harmless ways by way of replacing disgust with sympathy, rather like Voldemort affecting stuttering before he revealed himself, which would make evaluating his mental nature that much more problematic. The irony is that probably a large percentage of withdrawn people, even crazily withdrawn people, are so because they are afraid of people like AL, so I really think it would be a bad mistake to make it seem that AL's violence arose from some sort of inborn tendency toward social isolation. Medicating withdrawn people may just make for fewer people wary of chld molesters and killers.
I'm guessing the reason he didn't go after high school kids as in Columbine was that his murderous fantasies got less fun when older, e.g., when in high school, probably because (which he didn't realize, apparently) the natural rapist part of him had for many years been trying to tell him the point of violence and torture is control rather than death and partly because he was more into violating younger more impressionable and helpless kids. He probably thought to get the most fun he would need for the murders to be as much as possible like they were when he fantasized about them in the first grade, when they were likely most fun to him. Probably he killed himself because of his cowardice at getting shot by police, but still I'd say his murdering wasn't as pleasant a reliving of his first-grade imaginings as he had expected, because the murders really were senseless, the product of a deluded confused mind.
Not that I blame the media for having made Columbine a well-known topic. Sure, if naturally bad child-torturers had a better more sensible understanding of their rapacious natures less influenced by the hype that the violent like to surround themselves with to make themselves more scary, there'd be fewer senseless mass murders. But it might make for more effective rapists, which we don't need either. Discussions of violence can have good and bad effects (for humanity) on the naturally bad, whether the discussions are enlightened or stupid. But the typical, basically decent person can gain some useful (for humanity) understanding by not ignoring evil when it is of interest, just as it is mostly good for him to study whatever else that interests him.