Might get ugly in Civ.Ct. Well, it could.
I would never, ever shoot anyone in the back. Even here in Texas.
yeah, that's murder in most states. Morally/ethically though, I don't really have a problem with killing bandits one way or the other. If it were legal in my state, I would have done the same thing. Do you assume a bandit has a problem with shooting you in the back? Do you think soldiers don't get shot in the back all the time? Do you think LEOs don't shoot fleeing suspects in the back? If you are going to fight with monsters, you have to be prepared to become a monster. with apologies to Mr. Nietzsche .
If an armed perpetrator was running away from me and toward my daughter's bedroom, I would empty my gun into his back as fast as I could. If he was still standing, I would reload and shoot some more.
Just because a person shows you his back does not mean that he is surrendering, that he has given up attacking you, or that he is no longer a danger to you.