From PBS and Frontline: Last year Edward Snowden downloaded tens of thousands of top-secret documents from a highly secure government computer network. The revelations that followed touched off a fierce debate over the massive surveillance operations conducted by the National Security Agency. Now FRONTLINE investigates the secret history of the unprecedented surveillance program that began in the wake of September 11th and continues today. Through exclusive interviews with intelligence insiders, cabinet officials, and government whistle-blowers, Part One reveals how the U.S. government came to monitor the communications of millions of Americans and to collect billions of records on ordinary people around the world.