It's things like this that make me glad I live in small town Texas.
A few years ago, a woman I know was having trouble with a stalker. I was at her house one night when we almost caught him in her back yard. While she stayed at a friends house, me, her brother, and a couple of other friends stacked out at her house waiting to see if he would show up. We called the police, told them the situation, and told them what we were doing. They had trouble with this guy before, they just hadn't actually caught him doing anything. Before they left, one cop pulled me aside and said, "Stick some jewlery in his hand or something. Make it look good."
If someone breaks into your house, that is reason enough to believe force is justified.