The use of deadly force is justified, if the defender feels it is necessary to prevent a forcible felony, great bodily harm to themselves or another, or murder. It may also be used in the event that their home is violently broken into, and the defender believes that it is necessary to prevent harm to themselves or others. There is no duty to retreat as long as the person was not the initial aggressor.
Castle Laws are laws that address the use of force when defending one's self inside their home, or on their property. Some states expand this to vehicles, and the person's place of work. Castle Laws generally include: the places where this law applies, the requirements fro use of deadly force, if there is a duty to retreat, the amount of force that maybe used in defending one's self or others. These vary widely from state to state.