The drone strike that killed American-born cleric Anwar al-Awlaki was two years in the making, according to U.S. intelligence and Yemeni officials. They had tracked him for years, but he always evaded commando attacks and drone strikes. But three weeks ago new information made staying on Awlaki possible, and CIA drones were launched from a newly built secret base in the Arabian Peninsula. Meanwhile, the killing of Awlaki, along with a second American, Samir Khan, has reignited the debate over the legality of killing U.S. citizens suspected of terrorism, with the American Civil Liberties Union condemning the action. The strike may also have killed Ibrahim Hassan al-Asiri, the Saudi terrorist responsible for making the bomb that "underwear bomber" Umar Farouk Abdulmutallab carried in his underpants on a flight in 2009.