[LouAvul]

Here in Oklahoma our law specifically states: "Never point, or shoot your gun at a person unless 1) Your life is in danger at that moment, 2) The life of your mother or father, husband or wife, child or employee is threatened at that moment, 3) Your home is invaded and you believe the person will harm you or another person in your home, 4) Only the use of your gun could stop the harm or injury.

If I'm in a public place and I hear gunfire, I'm moving my loved ones and myself to the safest place possible. Sorry, our laws don't permit me shooting a perp to save a stranger's life.

[mylife]

And this Patchwork of gun laws and reciprocity can be very confusing.
More confusing than the scenario in the OP.

[Travis McGee]

Sorry, our laws don't permit me shooting a perp to save a stranger's life.

In every state I'm familiar with, you may use deadly force to protect a third party from death or serious bodily injury. There is no clause about not protecting "strangers" vice people you know or family members.