Obviously, it's debatable whether shooting a mugger is the result of defending property or life so I'll use another example. If I'm a clerk in a convenience and I see a shoplifter and shoot him after he has stolen some merchandise, without him ever having threatened me directly, I would not be justified. If, however, I brandished my weapon in order to prevent him from doing it, or threatened to shoot him, then that would be justified, because deadly force would not have been employed (Yes, it might seem extreme to threaten to shoot a petty thief, but the burden of proof would be on him to prove that I made the threat; furthermore, my property would still be intact).