Civilian vs. Law Enforcement Rules of Engagement

First watch this video of a encounter a LEO had with a armed drunk:

I posted the following over on The Shooting Bench Forums where you can read the other replies.

OK, first of all I agree the officer was justified in the use of deadly force and I’m pretty sure the bad guy owes him a pair of underwear!
Now with that said I’d like to play devils advocate and pose a question:  The officer moved towards the back of the vehicle and the BG took off on the run in the opposite direction and thus posed no imminent threat to the officer yet he drew his weapon and fired into the back of the fleeing vehicle.  Now the other side of my question, what if that was a civilian that stopped to render aid and the same thing happened, the BG shot, the civilian moved to the back and drew their weapon and shot as the van was fleeing in the opposite direction and posing no threat to the civilian.  In both scenarios the BG may pose a actual threat to other civilians since he is probably drunk and is obviously armed and dangerous.  Does this alone justify the use of deadly force by a LEO or Civilian?
What is boils down to what are the Rules of Engagement for LEOs vs. Civilians?  Are these rules actual laws or is it just a duel standard enforced by the judicial system?

Update on Wednesday, April 21, 2010 at 10:14 by Mike Jantz

I’ll add this one point.  It’s very easy to sit here in our comfy chair and evaluate the LEOs reaction and what he should of or should not of done but you really need to put your self in that position.  Your adrenalin is flowing, you just got shot at and your natural reaction is to eliminate the threat weather or not it is still a threat.

I think this would be similar point that could be made the pharmacist in Oklahoma that is facing charges for shooting a armed robber that was already shot and down on the floor. 

I think we need to apply a little human instinct to our judicial system when prosecuting victims of crimes that may of over reacted in protecting them selves.  What do you think?