Al-Awlaki moved to Washington, D.C., in early 2001 where he pursued further graduate education at George Washington University and served as the imam at the Dar al-Hijrah mosque in suburban Falls Church, Virginia. In Falls Church, al-Awlaki's services were attended by al-Hamzi and a third future 9/11 hijacker, Saudi national Hani Hanjour.
After the 9/11 attacks, the FBI interviewed al-Awlaki repeatedly. His telephone number had been found in the Hamburg, Germany apartment of Ramzi bin al-Shibh, a 9/11 planner now detained at Guantanamo Bay.
But just weeks after the terror attack, and days after he'd been interviewed by the FBI, al-Awlaki was invited to a private lunch at the Pentagon as part of an effort to reach out to the Muslim community. When asked by ABC News if al-Awlaki had actually attended the lunch, Pentagon spokesman Col. David Lapan said, "We believe that to be true."
"We believe it was hosted by a small group within (but not including) the Department of Defense General Counsel's staff," a Pentagon spokesman told ABC News.
Al-Awlaki left the U.S. for Yemen shortly afterwards. When he returned to the U.S. briefly in 2002, federal authorities again missed a chance to hold him.
The FBI had watched al-Awlaki after the 9/11 attacks, and were searching for a reason to detain to him. They observed al-Awlaki, who had already had two prior convictions for soliciting prostitutes, driving prostitutes from Washington across the Potomac River into Virginia. They considered holding him under the Mann Act, an obscure federal law that prohibits transportation of women across state lines for "immoral" purposes.
Ultimately, federal agents did not detain al-Awlaki or prevent him from leaving the U.S. They were, however, able to come up with a federal arrest warrant for al-Awlaki that could be executed should he return to the U.S.
Investigators found that the U.S.-born al-Awlaki had falsely indicated on his 1990 Social Security number application that he had been born in Yemen. Because the statute of limitations had passed, agents could not charge al-Awlaki with social security fraud. But since al-Awlaki had used his Social Security number to apply for a U.S. passport in Denver several years later, investigators believed he could be successfully charged with felony passport fraud. The alleged offense had occurred within the ten-year statute of limitations.
In October 2002, al-Awlaki passed through JFK airport. Authorities detained al-Awlaki, who was on a terror watch list. But they found they could not arrest him, because the day before he arrived in New York his arrest warrant had been rescinded by a federal judge in Denver at the request of the U.S. Attorney's office.
Shortly after he was released from JFK, al-Awlaki left the U.S. for good. From 2002 to 2004 he lived in the U.K. In 2004, he returned to family's home village in Southern Yemen. He has lived in Yemen ever since, where U.S. authorities said he was a recruiter for al Qaeda, a leading figure in al Qaeda's Yemeni affiliate, Al Qaeda in the Arabian Peninsula (AQAP), and the inspiration for terror plots in the U.S. and Canada.
Al-Awlaki had extensive e-mail exchanges with Maj. Nidal Hasan, charged with 13 counts of murder and 32 counts of attempted premeditated murder in the November 2009 mass shooting at Fort Hood, Texas. He praised Hasan in a published message soon after the shooting.
Accused "underwear bomber" Umar Farouk Abdulmutallab, the Nigerian charged with attempting to blow up Northwest flight 253 from Amsterdam to Detroit on Christmas Day 2009, met with al-Awlaki while training for jihad in Yemen, say U.S. authorities. Faisal Shahzad, who pled guilty to attempting to detonate a car bomb in Times Square in May 2010, has said he was inspired by al-Awlaki.
President Obama authorized the military and the CIA to kill al-Awlaki in early 2010, an unusual step given that al-Awlaki retains his U.S. citizenship. The ACLU and the Center for Constitutional Rights later tried, unsuccessfully, to challenge the government's right to put al-Awlaki on a hit list and freeze his assets. The Treasury Department's Office of Foreign Asset Control (OFAC) had formally labeled al-Awlaki a "Specially Designated Global Terrorist" so that it could freeze his assets.
Al-Awlaki responded with several internet messages that taunted President Obama and the U.S. military and called on U.S. residents to wage jihad against the U.S. In November 2010, he released a 23-minute video via radical Islamist web sites in which he said that any jihadi who wanted to kill Americans didn't need a "fatwa" or special religious permission, since Americans are the enemy and the "devil."
"Don't consult with anybody in killing the Americans," says al-Awlaki on the tape, sitting at a desk with an ornate dagger tucked into his belt. "Fighting the devil doesn't require consultation or prayers seeking divine guidance. They are the party of the devils."
The U.S. and Yemeni government had made previous unsuccessful attempts to kill or capture al-Awlaki. Officials said in December 2009 that they believed he might have been killed in a missile strike. In September 2010, Yemeni officials said they thought they had trapped al-Awlaki in a South Yemeni village, but then dropped that claim.
Less than a week after Navy SEALs killed Osama bin Laden in a raid in Pakistan on May 2, U.S. drones tried and failed to kill al-al-Awlaki in Yemen, according to U.S. officials. Unlike previous strikes in Yemen that have involved Tomahawk cruise missile launched by Navy ships, the May strike involved a predator drone.
Before his death, several U.S. officials said that al-Awlaki's ability to inspire lone wolf attackers made him one of the most dangerous men on the planet.