Obviously you disengage and call 911. You should also look around, because most housebreakings are done by groups, and they often leave a lookout in the street. The lookout is usually the least assertive or daring one, so if you get a good look at him and they catch him, he is most likely to squeal on his pals. You can also help catch the buggers if you get license numbers of unfamiliar cars.
The bastards who broke into my house in Houston got caught because our neighbor got a good look at their lookout and their car. They were tied back to other burglaries (they had stolen goods, including rifles, in their trunk when caught). The court sent all three of them to jail.