A terrorist attack in Texas by two U.S. citizens shows how hard it is to prevent such an attack -- even when one of the terrorists is well-known to the FBI. Anderson Cooper reports. David Martin explains why autonomous drones are being called the biggest thing in military technology since the nuclear bomb. Plus -- Imagine you're 5 years old and 1,000 miles away from home -- not knowing your last name or your address. How do you find your way back? Bill Whitaker has the story.