He was "bullied" is the new excuse for liberal/progressive nut cases.
It changes the perpetrator from evil criminal to hapless victim that deserves pity. ....
except the ones who started the trend in Columbine were also bullied - but then the problem was dissected, addressed and for almost 10 years the situation was relatively calm in that dimension until the recent shootings when it is obvious nobody is even attempting to address the bottom line issues but starts the hysteria about guns and gun control.
The recent incidents all over the US have been very different in their root causes - the most unpredictable and massive are connected to severe mental instability and it does not look like the perpetrators there have had any grudges particularly against the people attacked - it was basically a show, a random one.
But this case does not lok like that, because the student was looking for a particular teacher and had the history which can push to such reactions.
Personally, I think, that if the teacher would not run away - the negotiable solution would be quite possible. If the student would like just to shoot the teacher in revenge - he won't come to school, he would just wait for him in the bushes near his home.
The element of super drama and visibility clearly points that he, most probably, just wanted to threaten ( stupid as well) and not kill. The teacher's cowardice angered him and provoked to shooting randomly and suicide.
Putting all the incidents together does not serve the prevention of the problem solution at all - as prevention begins in the realization of the cause.