Sure does sound like the basement equivalent of a tree stand to me, from snacks & water to the camouflage of making the place look unoccupied on purpose.
Does he have the right to execute a person who is no longer a threat to his life? Short answer: No. That this is even up for debate is mindboggling. It's SELF-DEFENSE people, not the right to kneel over a seriously wounded, incapacitated person, mock them, put one in his/her hat, and then wait a full day just to be sure there is no doubt that they are dead. *That* is murder, and is just as ****ed up when a legal gun owner does it as it is when some junkie does it. Making the decision to live civilized is what separates us from them. Acting like them degrades the argument that you're better than them and it absolutely hurts our battle to protect our rights.
Somehow I don't think sitting in your boxers with a gun nearby, Cheetos in one hand and beer in the other while watching tv is the same as hiding in your house with supplies and firearms, most likely done up in the latest in tactical boots and drop holsters while luring in burglars. Even that isn't the thing that's wrong. It's the execution afterwards.