New evidence suggests that at least one convict escaped from Alcatraz and survived. National Geographic investigates one of the most intricate prison escapes in history - three tireless inmates break from the fortress-like 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? National Geographic goes inside the U.S. marshals' investigation following the complex and tantalizing leads they've tracked to close this case.