So what if the homeowners left their door unlocked. If you leave your keys in your car by mistake, is it still a crime if someone steals it? Yep.
Well, of course, but around here it's a crime to leave your keys in your car where a young child might take off with it and get hurt.
In almost every jurisdiction in the country if you leave your keys in your car and a child does take the car and get hurt your insurance company will help you out with the civil suit but not to the extent you imagined.
What we have here is a guy left his door open and shot the first person to come through the door. It may well have been a legal act but I wouldn't let the guy oversee my cash register!