I am looking at this based upon Kentucky law and cannot speak to the law of other states.
As for giving a warning, I agree with @Ouade5 with respect to the use of force continuum. Keep in mind that this is training given to law enforcement but is not always given to non-LEOs. The use of force continuum starts with physical presence and progresses, not necessarily in order, to verbal commands, open/closed hand strikes, less than lethal and then lethal force. It does not generally require the least amount of force necessary but that the amount of force be reasonable with respect to the threat.
While escalation of force should be similar for civilians, most of us walking down the street to not have a full toolbox on our belts to deal with every possible situation and, just as important, we do not have the same authority to detain or arrest a person.
As for this situation, I completely agree that ordering someone to stop or leave before firing is a good thing. It can be the difference between going to bed or going to jail, even if the force is justified. Long ago I was taught in our basic training to verbalize everything so the public hears you. “STOP, I don’t want to hurt you.” can go a long way when witnesses prepare statements or testify in court.
Now for the use of force in this incident. Again, based on Kentucky law and assuming all of the facts are true as described, this would be a justified use of force. The Kentucky use of force law is found in KRS 503.050 with the Castle and Stand your Ground doctrines are codified in KRS 503.055, included below in full. Assuming the person who was coming up the stairs was not one of those exempted under the statute, they are presumed to have entered with the “intent to commit an unlawful act involving force or violence.” Likewise, the occupant of the property is “presumed to have held a reasonable fear of imminent peril of death or great bodily harm to himself or herself or another when using defensive force that is intended or likely to cause death or great bodily harm” and has no duty to retreat.
The justification for the use of deadly force in KRS 503.050 is satisfied upon the presumptions created in KRS 503.055. This means that deadly force is presumed to be justified if a person breaks into your home or attempts to carjack you.
Under Kentucky law and based upon the facts presented, it appears as this would have been completely justified. It is interesting @Blacky about illegal entering being changed to a felony because under common law, where most US laws originate, was always considered a forcible felony for a dwelling. Likewise, a head shot is much more likely when you are shooting down a flight of steps at someone because it is the closest position to target and hitting the center of mass is much less likely. If the person was descending the stairs, there would be a higher likelihood of a shot to the groin or lower abdomen.
I agree with @Jerzy and and @Larry130 about giving the warning. There will always be those instances where “it depends” is the absolute right answer. Yes practice giving warnings but do not put your life in more danger by doing so. But, if you are in this situation, you probably won’t have time to call your lawyer before deciding what to do. Know your laws and act accordingly.
@Todd30 I would add, “that door was locked for your protection, not mine!”
Thanks @Blacky for teeing me up on this one!
503.050 Use of physical force in self-protection.
(2) The use of deadly physical force by a defendant upon another person is justifiable … only when the defendant believes that such force is necessary to protect himself against death, serious physical injury, kidnapping, sexual intercourse compelled by force or threat, felony involving the use of force, or under those circumstances permitted pursuant to KRS 503.055.
503.055 Use of defensive force regarding dwelling, residence, or occupied vehicle – Exceptions.
(1) A person is presumed to have held a reasonable fear of imminent peril of death or great bodily harm to himself or herself or another when using defensive force that is intended or likely to cause death or great bodily harm to another if:
(a) The person against whom the defensive force was used was in the process of unlawfully and forcibly entering or had unlawfully and forcibly entered a dwelling, residence, or occupied vehicle, or if that person had removed or was attempting to remove another against that person’s will from the dwelling,
residence, or occupied vehicle; and
(b) The person who uses defensive force knew or had reason to believe that an unlawful and forcible entry or unlawful and forcible act was occurring or had occurred.
(2) The presumption set forth in subsection (1) of this section does not apply if:
(a) The person against whom the defensive force is used has the right to be in or is a lawful resident of the dwelling, residence, or vehicle, such as an owner, lessee, or titleholder, and there is not an injunction for protection from domestic violence or a written pretrial supervision order of no contact against that person;
(b) The person sought to be removed is a child or grandchild, or is otherwise in the lawful custody or under the lawful guardianship of the person against whom the defensive force is used;
(c) The person who uses defensive force is engaged in an unlawful activity or is using the dwelling, residence, or occupied vehicle to further an unlawful activity; or
(d) The person against whom the defensive force is used is a peace officer, as defined in KRS 446.010, who enters or attempts to enter a dwelling, residence, or vehicle in the performance of his or her official duties, and the officer identified himself or herself in accordance with any applicable law or
the person using force knew or reasonably should have known that the person entering or attempting to enter was a peace officer.
(3) A person who is not engaged in an unlawful activity and who is attacked in any other place where he or she has a right to be has no duty to retreat and has the right to stand his or her ground and meet force with force, including deadly force, if he or she reasonably believes it is necessary to do so to prevent death or great bodily harm to himself or herself or another or to prevent the commission of a felony involving the use of force.
(4) A person who unlawfully and by force enters or attempts to enter a person’s dwelling, residence, or occupied vehicle is presumed to be doing so with the intent to commit an unlawful act involving force or violence.