Overview: It's 1961. Air traffic controllers and local dignitaries in Ndola, Africa await the arrival of UN Secretary General Dag Hammarskjold, flying in on a top-secret peace mission. But the plane never arrives, and is found the next morning crashed and burning just a few miles from the airport. For decades, conspiracy theories have suggested that the plane was shot down. Now, startling new claims from a former U.S. intelligence officer have triggered a new investigation to get to the bottom of this controversial, decades-long aviation mystery.