In general, deadly force may not be used to simply defend ones property, and can only be used to defend someone's life or safety. An unarmed thief who has grabbed a cash box right in front of the landlord and then tries to immediately run away is not a threat to one's life, and shooting him to stop him would be highly illegal.
Depends on the state you live in.
I believe TX allows you to blow someone away if they are stealing your property.
I remember a bit before Katrina, there was a case in New Orleans East I think, a couple of kids were in an apartment parking lot, stealing stuff out of a car. The owner shot them and killed at least one of them, from his upstairs balcony facing the car.
The actually tried to press charges on the property owner, but they couldn't find a jury that would convict him....and I agree.
If the kids hadn't been committing a crime, they'd still be living today.
But most states I know of..if your able to in any way at all, think you are threatened, you can shoot someone, and no one shoots to injure, you're a fool if you try doing that. Heck, some states have weird old laws too, I remember in AR, that if you see someone trying to commit arson, even if you are not the property owner, you can legally shoot that person.
Things like that...