Tour the deep dark world of the East German state security agency known as Stasi. Until the fall of the Berlin Wall in 1989 the Stasi, masterminded a system of surveillance that kept the country under control for decades. Hubertus Knabe studies the Stasi — and was spied on by them. He shares stunning details from the fall of a surveillance state, and shows how easy it was for neighbor to turn on neighbor. Watch »Trust