Hard to say what was going through this officer's mind when the perp made a run for it. Willie (Walter Scott) wasn't very fast to begin with, easy to spot (fat black guy green tshirt missing a shoe), the middle of the day, no weapons, no warrants beyond a child support bench warrant, so what was the point of shooting him?
It doesn't look like there was any rage, he just mater of factly shot the guy. Forget the racism bull shit. There is no indication that this officer was a nego hating racist. Just a guy who mad a bad choice.
My thought is lack of training. Major lack of training.