I've always wondered what you should do if you hear "Police... we have a warrant". If I was the badguy in someone else's home, and I sensed there would be a confrontation, that's what I'd do.
I would say: "Ok. I'm talking to the police department (911, dispatch, whatever) right now. If they confirm that you are indeed who and what you say you are, I will stand down and you may proceed safely. Otherwise, stay where you are and wait for the "real" police."