If some idiot ran me off the road and pulled a gun on me and my wife, I wouldn't shoot to wound the son of a b!tch, I'd shoot to take him down. And such a shooting would be absolutely, 100% justified.
The thing is because he is a police officer he will naturally tend to sway the jury and the judge his way. I bet he will show up in his uniform and act all professional, exactly opposite of the way he acted on the side of the road.