Store owner and customer are both lucky they didn't hit the BG,  UNLESS they had witness / or could prove the departing BG were an immediate threat to other people being killed or grievous bodily harm from fleeing BG... Because they (store owner or customer) could be charged with a Felony (done with a Gun in Florida, it's mandatory Jail Time under min sentence guidelines where Judge has no choice but to send you to jail for taking Law into their own hands by shooting BG).   Once the original BG assault is done and BG is Fleeing, that activity is over.    (Ex: A person was attacked in front of many witnesses by a BG using a knife, where the innocent person received a number of serious knife cuts before he managed to get the knife away from BG and the Victim proceeded to use BG's knife to do some cutting of his own on the BG.   Even though Victim was hospitalized briefly and received quite a few stitches;  GUESS WHO WAS CHARGED, RECEIVED PROBATION and FORCED to PAY restitution for the BG's hospital bills and BG lost time from work?   THE VICTIM!   First assault was over (BG did get a small slap on wrist for his assault and some of Victims Money owed TO BG was reduced.   FAIR?   NO way, but the Law is strange at times..  

Moral of Story... understand your State's Laws on When you can legally use deadly force.   Regardless of how YOU will deal with such a situation, at least know what you're facing.... another view from my saddle and not intended to give legal advise; you should consult with an attorney in your state.    davzay