When my husband took the computer back to Best Buy, they printed him out a receipt to prove it was returned. And on that receipt was a phone number and email address that wasn't his. So either the thief put in his own information (which would be nutso), or he made up a random bit of information to throw people off the track. My husband - ever clever - figured out that the email address and number belong to a man who lives not far from us. He gave MasterCard the information to follow up on, and the MasterCard service person said, "You've done more for us today than we've done for you!"
Hopefully one more thief will soon be out of commission.