Apparently, the key to the whole operation was finding and tracking Bin Laden’s most trusted courier, a process that took years — and involved info given by Guantanamo detainees: Sunday afternoon’s raid by U.S. forces that killed Osama bin Laden was the “culmination of years of careful and highly advanced intelligence work,” senior administration officials said in a conference call, describing the genesis of an operation that sounded like it was right out of a “Mission Impossible” movie. Some time after Sept. 11, detainees held by the U.S. told interrogators about a man believed to work as a courier for...