In the aftermath of the Boston Marathon bombings, the threat of terrorism again confronts Americans. More than a decade after 9/11 and hundreds of billions of dollars later, there are pressing questions about whether America's investment in its "terrorism industrial complex" has made us safer. In this program, FRONTLINE's Pulitzer Prize-winning reporter Dana Priest traces the journey from 9/11 to the Marathon bombings and investigates the secret history of the 12-year battle against terrorism.