it is an imaginary scenario only, just an example.
A robber robs a house, and take hostage of the house owner's son, the owner request the robber to leave the child but he refuses, so the owner shot the robber to rescue his son.
Owner killed the robber so it is a crime but considering the situation and circumstance, it is not a crime.
so can we use the term like " circumstantial innocent" for him?
The problem for me is that shooting the robber/hostage-taker in this situation is likely not a crime. I don't mean to get too literal here, but I'm having a problem imagining the person for whom you're looking for a name, so thinking up a name is difficult.