Shooting somebody in the back isn't illegal in and of itself. Just because you don't agree with the decision not to prosecute doesn't mean the shooting was bad.
As for Scott, prosecutors did say that the shooting was justified and for their scope, that is no wrong doing. If it makes you feel better, no criminal wrong doing.
"If you look through your scope and see your shoe, aim higher."
-- said to me by my 11 year old daughter before going out for hogs 8/13/2011