what would I have done??
I would have drawn and started quickly moving towards the shooter, while trying to maintain cover (cars). When within a tactical handgun range, I would yell at shooter to make sure he not a leo, once determined he is not a leo, and no innocent bystanders in my way (or behind him), and he does not immediately cease his threat toward me or others, I would empty my magazine into him. If he got away, I would do everything to follow him in my vehicle and use cell phone to lead police to him.
I know, here comes the John Wayne remarks...
I dont see it as ego, I see it as duty. I don't like it, and I hope I never have to answer that duty. But, I feel that being a MAN, and having a gun, and being well trained to use the gun; it is my duty to protect the lives of anyone from an evil person wanting to do them serious bodily harm or death.
Notice I said 'I feel'. I did not say other people are wrong if they feel otherwise.
I could not live with myself sitting back and being a good witness while someone's mother, daughter or son is being murdered, when I could have stopped it.
I would follow him, because he needs to be taken off the street.