Being a jerk led to his shooting of all those people but that doesn't make good headlines, support a political view, or clean up the mental situation so that people can easily explain the violence.
Actually, claiming that he was a "jerk" instead of even acknowledging the possibility this might be related to PTSD supports the dominant political position. Many people assume we can send our soldiers off and bring them home and there will be no social/emotional consequences. This idea is actively promoted by military industrial complex. It allows people to easily explain away events like this so they can support the political views that promote the maintenance and expansion of global American hegemony. Acknowledging the brutal social and emotional effects of war on people and actually questioning the policies that place so much stress on people is FAR more difficult then simply calling the "perp" a "jerk" and dropping it.
In fact, I would say that the characterization of symptoms that are common with PTSD as "jerky" does far more harm to the people who need help because now it all gets explained away as defects in character.
It's time for American's to get real about the effects of these wars. Elder999 was right, we're going to see a lot more of this. Violence springs back on the people that perpetrate it...especially when you're on the wrong side of morality.