They identified him as one of Bin Laden's couriers, an aide the terror chief trusted with his life. But details were scant and agents quickly found the trail went cold. It was not until 2004, when Al Qaeda operative Hassan Ghul was captured in Iraq, that the CIA began to make progress. Ghul told the intelligence service that al-Kuwaiti was a courier and that he was close to Faraj al-Libi, Al Qaeda's operational commander, who replaced Khalid Sheikh Mohammed.The pace of the pursuit then picked when U.S. soldiers captured al-Libi. Under CIA interrogation, al-Libi admitted that when he was promoted...