Someone who takes care of such things recently offered me the following scenario, asking if it would be appropriate to draw down on someone with a gun and, indeed, shoot him, that is, with no further information provided and action being immediately necessitated because of what had just happened (this being a trick question):
Say you, the priest, are outside the front entrance of the Church greeting visitors to your tiniest of all tiny parish churches in the middle of absolutely Nowhereville. Say that as you’re chit-chatting two shots and then immediately a third ring out inside the church and you rush into the entrance of the church, being immediately faced only a second later with a fellow whom you’ve never seen before holding a gun in his hands, looking very emotionally overwhelmed, splattered with blood, but himself not being injured that you can see… Can you, should you, must you shoot him?
The answer of course is absolutely not until more information, perhaps all provided in the next nanosecond, is to be had.
In our little church in which so very many are armed and well able to defend themselves or others, whether visitors or not (we get a lot of very very capable visitors btw), my first thought would be that some ne’erdowell had begun to shoot others (the first two shots), and that the third shot was from a good guy who was defending the innocent. Although he had the capacity and opportunity to shoot again, and indeed, his gun was pointed in my direction at low ready, this fellow may have no intent to do any more shooting as he had already ended the threat, merely having acted in the defense of others, but being ready for any other bad actor to enter the scene. But I don’t know yet whether he’s a good guy or a bad guy.
If he raises his gun at me, some action may be necessary. But if, considering me to be no threat, raises it up towards the congregation, well, I still don’t know. That behavior would tell me that there may be more than one perpetrator and he’s seen another raise his gun to shoot non-weaponized parishioners. Assessment is necessary, and in this case would only take another 1/2 second. You don’t want to take out the good guy while he’s stopping mortal threats.
The subsequent information gathering will be important. Meanwhile, even if he’s an apparent good guy, his gun is to be confiscated until the police arrive. Criminals and especially terrorists are particularly scrupulous about leaving no one alive in their own group who might be able to rat out others and/or any connections, the whereabouts of computers, phones, etc. Killing your own and then oneself is often the modus operandi of such people.
Hopefully, it can be seen from this story just how important scenario based training is.