[gvf]

The need to shoot - which has to be to stop an imminent lethal attack - would, if it existed, already have been proven: the OP, having refrained from action to stop that attack, would not be posting because he would have been killed or grievously injured. He wasn't, he's fine, there was no attack. He judged aright

On top of this: he was there.

Second guessing a positive outcome of a situation you weren't involved in? Kind of wacky. Especially as it involves killing people.