Al-Awlaki was at the heart of one of the most dangerous terror groups on earth . Growing up and living in the United States gave him a unique understanding of U.S. society . He mocked U.S. intelligence for not picking up his e-mail traffic with Maj. But at some point he became disillusioned with his adopted country -- perhaps because of a series of encounters with U.S. law enforcement over his alleged use of prostitutes . Nidal Malik Hasan, who killed 13 people inside Fort Hood last year. He had escaped at least two previous attempts to kill him .
Al-Awlaki was at the heart of one of the most dangerous terror groups on earth . Growing up and living in the United States gave him a unique understanding of U.S. society . He mocked U.S. intelligence for not picking up his e-mail traffic with Maj. Nidal Malik Hasan, who killed 13 people inside Fort Hood last year. He had escaped at least two previous attempts to kill him .