Funny thing is that when someone starts shooting people tend to clear out as fast as possible. You can see it on the videos. Shooter starts out with five people within ten feet and after the first shot the smart one try to run away or go to the ground. That leaves the shooter all alone and they start moving towards large concentration of victims, firing as they go. I won't take a shot unless I think it's clear or I am returning fire. I suspect almost every shooter would find it much harder to shoot well if he was getting return fire. If nothing else it will force him to find some cover or slow down his rate of fire as he tries to figure out where my fire is coming from. That time could let others get away.

I did stop a robbery at a convince store many years ago. For that I used a 12 ga shotgun. Super weapon to convince a perp to lay down his gun, lay down on the ground and make snow angels lest he get shot. At 15-20' that 12 looked like a tank gun. City of Baltimore plea bargained that down to misdemeanor. Time served for the perp. And they wonder why crime happens.