I am from that area, and my guess is that he WAS harrassed for 5 years by this kid and his family. There are a LOT of ignoramusses there, and it's not just the killer.
Keep in mind we don't have all the facts to this case. However I do believe there is more to this - The guy has that resigned "there is no point in living" look on his face. Of course shooting a kid is ridiculous, but having said that, some kids can just be horrible. Everyone talks about how "good" they are, but in fact, they can be monsters. We had a boy like this is our old neighborhood, and he was downright nasty, cruel, and loved to tear stuff up. His parents of course thought him to be an angel, and his mother routinely threatened to sue the school if they disciplined him or he got low grades. It's was always the school's fault, don't you know.
This kid at the age of 12 went into some guy's house while he was on vacation and vandalized the heck out of it, smashing windows and tearing up stuff. All the kids said he did it, but you never heard another word.
This kid might have done the same to this old guy, and he just took it until he snapped (he probably wasn't very level to begin with).
It's just a sad fact of life that a lot of kids don't seem to learn. If you push the wrong person, they might push back.
The guy was wrong no doubt, but I'll be willing to bet the kid would be alive today if the parents had taught him to respect. That's what is missing today.