NGC investigates one of the most intricate prison escapes in history three tireless inmates break from the fortresslike Alcatraz Island Federal Penitentiary and brave the frigid waters in a handmade raft. For nearly 50 years, it was assumed that these men drowned, but what if they didn't? NGC goes inside the U.S. marshals' investigation following the complex and tantalizing leads they've tracked to close this case.