Seems that the man was at a Sonic and a BG walked up to his window and shot him in or near the neck and took off running. The strange thing was that her husband who was with the man, flagged down an LEO and pointed to the BG running and briefly described what happened. The LEO's response (after seeing the masked BG running) was something like, "I can't go after him until I get a lot of paperwork done first." BG got away and was never found. All I have on the details is her word of what happened.
Her question to me was, "With the laws as such, if my husband had been armed, could he have shot the BG?" My initial response was, "Of course." But then she added, "It happened so fast, that by the time my husband could react, the BG was running away."
This caused me to pause. During the assault - Sure. But now the immediate threat is over, there was Intent, Opportunity, and Ability, but now that he has turned to run and it is not my car, home, or business.....?
My rational side says - may not be justified. My emotional side says

Aside from the fact that shooting a running target in a populated area where a Sonic is likely to be is a bad idea, what is the legality?
Opinions please.