Larry should have been punished for his stalking like behavior, but Brandon (the shooter) had no justification what so ever to shoot him. Murder can never be justified.
No but it can be explained.
He ended up in a place for troubled teens, and sexually harassing them with the most disgusting behavior can easily push them over the edge. It's not the first time a freak pushed someone over the edge with their sexual predation.
Teachers should have seen it coming... but if they couldn't stop the kid from poking holes in his room with a screwdriver, they probably couldn't stop him from grabbing butts and crotches either.