The would-be bomber revealed Monday to have been plotting to blow up an American airliner with an underwear bomb was said to be a double agent, American officials said Tuesday. The agent infiltrated the terrorist group and gathered highly sensitive information on its operations, including the innovative bomb and its designs, delivering all of the intelligence to the CIA. He reportedly spent weeks in Yemen at a dangerous al Qaeda outpost, giving the U.S. the information it needed to kill Fahd Mohammed Ahmed al-Quso, a suspect in the 2000 bombing of the USS Cole. He handed the bomb to top explosive experts and the FBI to allow analysis of its complicated workings. Officials would not identify the operative, nor where he was from.