He never had to aim at his head, nor go and pump five rounds in. Even shooting someone in the thigh, can be lethal; aiming at a nut or something. Even then, you should help them out, or at least call 911 or your countries emergency service #. In my state, it's the minimum necessary protection allowed and no more than that. Not a head shot, the five more rounds, surely some of that is ***** of a corpse.
Well if you don't want to run the risk of getting shot, don't draw down and attempt to rob people who may be packing.
That said, the shop owner has the right to **** in self defense but not ****** in anger.