I've read about the "21 foot rule" and all that, but this statement raises a question in my mind. If the aggressor is standing there, holding a knife, but not making any move or other aggressive actions toward you or another person, do you fire?"During the course of the stabbing incident an off-duty security officer who was armed interceded. He produced a weapon and ordered the suspect to drop the knife. And when the suspect did not comply, he shot the suspect," said Boston Police Commissioner Ed Davis.
I suppose the situation here was clear that he had just stabbed the doctor, so failure to immediately surrender does pretty much put them in the role of aggressor, even if they are not presently "aggressing". And if the victim was still present, then the presence of the still-armed aggressor does prevent help from reaching the victim.
I guess I wonder what if the person was deaf or did not understand English? Of course seeing a gun in their face is a universal language, but I wish the report had provided more details about the demeanor of the attacker just prior to the shooting...