It doesn't matter if the guy walked in from outside into his home (castle) and caught the buggers in the act. Just because he was not in his residence at the time that CRIMINALS entered it, does not mean it is no longer his residence(castle). He still have every right afford to him to use deadly force. The reasoning for castle doctrin is so VICTIMS don't have to second guess an intruders intentions and can immediately asses the threat as one that will result in the bodily injury or death of the lawful occupant of the home.
Anyways, YEAH for the weekend
