Mary-Kate Olsen is off the hook. Federal prosecutors have decided not to pursue a criminal case into how Heath Ledger obtained the slew of painkillers that caused his death in January. See a photo retrospective of Heath Ledger's life. Prosecutors in the U.S. attorney's office in Manhattan had been overseeing a Drug Enforcement Administration probe into whether the drugs were obtained illegally. But the prosecutors nixed the investigation "because they don't believe there's a viable ...