Pervasive Medicare Fraud Proves Hard to Stop

The ordinary looking office building in a suburb of Baltimore gives no hint of the high-tech detective work going on inside. A $100 million system churns through complicated medical claims, searching for suspicious patterns and posting the findings on a giant screen.

Hundreds of miles away in a strip mall north of Miami, more than 60 people — prosecutors, F.B.I. agents, health care investigators, paralegals and even a forensic nurse — sort through documents and telephone logs looking for evidence of fraudulent Medicare billing. A warehouse in the back holds...