The correct answer is "as soon as you figure out what's going on, you ask to speak to your lawyer":

http://boingboing.net/2008/07/28/law-prof-and-cop-agr.html

I expect that your lawyer will then explain the situation to the cops, point to your car in the parking lot, point to your lack of criminal record, motive, or experience in fencing stolen cars, offer a stirring and heartfelt apology on your behalf, and then stand by to argue.

(But I can't be sure of that, because I am not a lawyer myself.)