Depends on the situation entirely.
Was it in self-defence/the defence of another when your/the other person(s) lives are at risk? Yes, it is a justiflied killing.
Was the victim someone whom has committed an unforgivable act, like a murderer or a dictator? Maybe, this situation depends on your point of view.
Was it a murder of someone over something as trival as money/material goods? No that is an unforgivable act and you should rot in prison/be on death row.
Was it in self-defence/the defence of another when your/the other person(s) lives are at risk? Yes, it is a justiflied killing.
Was the victim someone whom has committed an unforgivable act, like a murderer or a dictator? Maybe, this situation depends on your point of view.
Was it a murder of someone over something as trival as money/material goods? No that is an unforgivable act and you should rot in prison/be on death row.