Lots of good ideas here.
One that keeps coming up recurrently is the parents. But there have been bad parents since the dawn of time. I knew kids that had alcoholic, abusive parents, and they had their issues to be sure, but none of them, (that I know of), tried to kill anyone. Another girl I grew up with had "pillar of the community" parents, her father was a police captain, and she was a complete whore.
My point is, that I don't think that social dynamics between parents and children and children and their peers have fundamentally changed. Kids will always get picked on and kids will always have bad parents. But what has happened in this last couple of decades, that drives children to murder?
Our perception of people isn't the same as the perspective of the members of these families. If a parent is strict publicly, I suspect they're more strict privately. A friend from the time I was about 4 hung out with the Greasers when we were in high school and got in a fair amount of trouble. Drinking, drug use, he had a party when the parents were out of town and when a neighbor called the parents about the noise, he said "Make the call", meaning call the police. They busted up the party, found underaged drinking, drugs and hauled the kid off. His sister was the model straight A student, cheerleader, good girl type as far as I know and I don't remember her ever being in any kind of trouble. BTW- the dad joined the local PD in 1960 and he was the Captain at the time of this party. A friend of the son decided to do some snooping while everyone else was in the basement, so he went into the parents' bedroom and found one of the dad's service revolvers, so he took it, eventually using it in a robbery. To make matters worse, when it looked like he was in deeper than he could get out of, the friend of the cop's son blew his brains out on a park bench with that service revolver.
The parents married VERY young, had kids VERY young and had some loud fights. They didn't seem to care if anyone heard them, either. One day, a lamp flew out the back window and I'm not sure anyone expected them to stay together, but they did. They eventually reached a point where they stopped fighting and have gotten along great ever since. The son seems to have gotten through the rebellious period (it took a long time) and the daughter has parties where they drink an awful lot. The rest of the family is right there, too. Oddly enough, the son eventually moved to PHX and was soon followed by the parents and sister.
I saw them spank the kids and I saw others that didn't. The guy who killed himself was a PITA from the day I met him but his sister was really nice.
If we aren't there to see everything, we can't know who'll be good or bad and it's like any other personality conflict- not everyone gets along but sometimes, it's the parents and kids.