There is no duty to retreat inside one's home, or place of business. For deadly force to be justified it must be in defense of one's self or others. The person must believe that there is a real threat of death, or bodily injury, and all other means of defusing the situation must have be exhausted before using deadly force. Deadly force may not be used in the sole defense of property.
+Q: Does Wisconsin have a "stand-your-ground" law?