Back to the situation at hand, I'm frankly troubled that nobody agrees that a shooter who quickly offs himself is about the best outcome. Respectfully, I would like someone to describe a better outcome for the case here.

OK, for the sake of argument, let's say you killed this shooter before he committed the domestic violence. There are at least three problems with that outcome: (1) the wife will most likely be pissed at you for killing her husband and will want you locked up; (2) you then have the most important witness saying the shoot was not justified; and (3) you have to live with knowing you killed a person.

More moving parts...