I think he's extremely self-respecting
to the point of excess. I think he's doing this as an ego-exercise: "See how smart I am, I can kill at will and no one can catch or stop me."
I just heard a witness say that the 2nd shooting at the Michaels store was on the order of 200 yards. That's hardly a long shot by sniper standards. Any semi-qualified hunter could make that shot, especially if the weapon had a scope. Every Army grunt routinely trains at 300 meter targets using standard M-16 sights. It doesn't take military training to hit someone at 200 yards with a 5.56mm round.