Murder is justifiable for a bag of popcorn?
Seriously?
The next time a cop stops you get three feet in front of him, jump at him, start screaming at him and then through a big container of popcorn in his face all at the same time and see just how many times he shoots you. My educated guess is that he will stop shooting when you hit the ground.
That is what cops are trained to do, stop a threat and they only have to believe that it is a threat of great bodily harm or death to them. That decision will be made in a fifth of a heartbeat.
I'm not saying what this retired cop did was right but the situation leading up to it put him in a reactionary situation/position. I would not be surprised if he walks.