The profile is ex-marine sniper, dishonorably discharged, with some kind of vendatta against the "establishment" in Washington.But, but... murderers, rapists, and pedophiles -- ex-cons, all, to boot, in your scenario -- are hardly "the establishment"!
The part I don't understand is why someone picks John Q. Public to attack? If I had this kind of shooting experience and chose to kill people like a madman, I'd probably take care of a few killers, serial rapists, pedaphiles, etc. [...]
Wouldn't it be even more logical for him to go after politicians, members of the military (primarily officers, "the bastards who shitcanned me"), and perhaps policemen (and -women), if it were truly "the establishment" he was pissed off at?