76-2-405. Force in defense of habitation.
(1) A person is justified in using force against another when and to the extent that he reasonably believes that the force is necessary to prevent or terminate the other's unlawful entry into or attack upon his habitation; however, he is justified in the use of force which is intended or likely to cause death or serious bodily injury only if:
(a) the entry is made or attempted in a violent and tumultuous manner, surreptitiously, or by stealth, and he reasonably believes that the entry is attempted or made for the purpose of assaulting or offering personal violence to any person, dwelling, or being in the habitation and he reasonably believes that the force is necessary to prevent the assault or offer of personal violence; or
(b) he reasonably believes that the entry is made or attempted for the purpose of committing a felony in the habitation and that the force is necessary to prevent the commission of the felony.
(2) The person using force or deadly force in defense of habitation is presumed for the purpose of both civil and criminal cases to have acted reasonably and had a reasonable fear of imminent peril of death or serious bodily injury if the entry or attempted entry is unlawful and is made or attempted by use of force, or in a violent and tumultuous manner, or surreptitiously or by stealth, or for the purpose of committing a felony.
So, it gets down to the question of "reasonableness," and on this subject, Utah law states:
(a) the nature of the danger;
(b) the immediacy of the danger;
(c) the probability that the unlawful force would result in death or serious bodily injury;
(d) the other's prior violent acts or violent propensities; and
(e) any patterns of abuse or violence in the parties' relationship.
Let's hope the homeowner gets a reasonable judge. Things such as the age and infirmities (if any) of the homeowner, the burglar's previous criminal history, etc., will undoubtedly come into consideration.
I'm not going to judge when I don't know all the facts, but I do know that the homeowner would have been on more solid ground had he shouted a warning, and then, being ignored, waited until the perpetrator had actually opened the door.
Bullseye