Reminds me of a real incident in the US a few years back: police chief at home quietly watching TV. It is a dark suburb, who knows who roams around at night. He hears some noise at the back door, does not lose a second, picks up his gun goes back there and shoots (never mind looking first: who knows, could be a bad guy who will kill first). Turns out he killed his son who was coming over on an unexpected visit.