Some murder cases lie unsolved for 20 or 30 years, gathering dust in a back room. But the Metro Police Department is dusting off those files and tracking down suspects - suspects who think their crimes are long forgotten. They've solved 9 cases in one year - one of the highest rates in the country. But how do you solve a cold case? How do you handle evidence that's 20 years old? We talk to Metro's head of violent crimes, plus a DNA scientist, on how they're solving old cases, arresting suspects, and helping families lay ghosts to rest.