My non-lawyer opinion of the below statute is that it is not acceptable in WI to use deadly force solely for the purpose of defending property, however, as was mentioned it has been testified that the purpose of the firearm was for the purpose of self defense. Wisconsin s. 939.49 Defense of property and protection against retail theft. "(1) A person is privileged to threaten or intentionally use force against another for the purpose of preventing or terminating what the person reasonably believes to be an unlawful interference with the person's property. Only such degree of force or threat thereof may intentionally be used as the actor reasonably believes is necessary to prevent or terminate the interference. It is not reasonable to intentionally use force intended or likely to cause death or great bodily harm for the sole purpose of defense of one's property. (2) A person is privileged to defend a 3rd person's property from real or apparent unlawful interference by another under the same conditions and by the same means as those under and by which the person is privileged to defend his or her own property from real or apparent unlawful interference, provided that the person reasonably believes that the facts are such as would give the 3rd person the privilege to defend his or her own property, that his or her intervention is necessary for the protection of the 3rd person's property, and that the 3rd person whose property the person is protecting is a member of his or her immediate family or household or a person whose property the person has a legal duty to protect, or is a merchant and the actor is the merchant's employee or agent. An official or adult employee or agent of a library is privileged to defend the property of the library in the manner specified in this subsection. (3) In this section “unlawful" means either tortious or expressly prohibited by criminal law or both."