DEPARTMENT OF SELF-REFUTATION:

[A] document from the 9/11 Commission records at the National Archives, declassified at my request, shows that a few days after Ammar's arrival, the manager of an escort service called Awlaki to warn him that he had been interviewed by Wade Ammerman, an F.B.I. agent, who had asked about the imam's visits to prostitutes. It was clear from Ammerman's questions that the F.B.I. knew everything.

Awlaki's panic, his sudden agitation about the course of his life, does not appear to have been triggered by American hostility to Muslims. Rather, he seems to have realized that his own un-­Islamic behavior had put his career success and family comity at risk. If the bureau charged him, or leaked the files, he might instantly lose the moral authority he brought to public arguments over the war in Afghanistan or the dubious roundup of Muslim men. If the F.B.I. chose instead to threaten exposure to coerce his cooperation, that might be even worse. Within a few days, he was gone, and he would never live in the United States again.

Despite the danger that he perceived from the prostitution dossier, Awlaki did not immediately give up on the possibility of resuming his American life. Awlaki was hardly in a position to tell his family about the menacing F.B.I. file, and his father pressured him to return to Washington and resume work on his Ph.D. Awlaki returned for one visit, in October 2002, but uncertain of the F.B.I.'s intentions, he did not dare risk staying. In fact, though he had no way of knowing it, F.B.I. memos from 2002 show that officials were exploring the possibility of charging Awlaki with a prostitution-related offense. A year after his visit, in the fall of 2003, he astonished F.B.I. agents by calling the bureau's Washington field office out of the blue, expressing a desire to meet in London or Sana to clear up any suspicions, possibly as a prelude to returning to the United States. He mentioned media reports tying him to 9/11 because some hijackers had visited his mosques, which he called ''absurd''; presumably he also wanted to find out whether the bureau planned to act on the prostitution file. But the F.B.I. treated the issue as a low priority, and when Awlaki stopped answering emails, plans to meet in London fell through, records show. As late as 2004, when Awlaki returned to Yemen for what would prove to be the remainder of his life, he would sometimes suggest to family members that he might still move back to the United States. ''He would always say, 'Thank God I'm an American citizen and I have a second home to go back to if things go wrong in Yemen,' '' his uncle, Saleh bin Fareed al-Awlaki, told me.

It is a tantalizing period, hinting at an alternate history. What if the F.B.I., recognizing Awlaki's influence and value as a mediator with the Muslim community, had assured him that there was no plan to use the prostitution evidence to charge or embarrass him? What if he had resumed his life in Washington and continued to grow into an important public figure? Might he have become a responsible leader, a voice in the debates over the wars in Muslim countries, the wisdom of drone strikes, the fate of Guantánamo? Might he never have joined Al Qaeda? The contemporary history of terrorism, not to mention his playlist on YouTube, could have unspooled quite differently.

Instead, Awlaki's ambition took a new and more militant path. At first subtly in 2003, while in Britain, and more clearly after 2005, his rhetoric became increasingly ferocious, his embrace of violence more open. After moving on to Yemen, he was arrested in 2006 and held for 18 months without charges at least in part as a result of American pressure. Not long after his release at the end of 2007, angered by the Yemeni surveillance teams constantly following him around Sana, he would depart for his family's ancestral home in Shabwah province, also the hideout for Al Qaeda in the Arabian Peninsula. Within months he would be part of the group and, soon after that, deeply involved in plotting attacks on America.

In 2010, when Obama ordered a legal review and then approved the killing of Awlaki, some civil libertarians objected, saying that he was being denied his constitutional rights as an American citizen. But some Muslim commentators publicly expressed caution for more practical reasons. One was Mohamed Elibiary, a security consultant and a law-and-order Texas Republican. ''It was very clear, at least to me, that if you're trying to fight a martyrdom culture, you don't go make martyrs,'' he said. ''I'm sorry to say, I think I was right.'' In recent years, Elibiary has regularly interviewed Americans charged with terrorism for the federal public defender's office. ''In that world, to the last person, you find that they're convinced that Anwar al-Awlaki is a good guy and a martyr,'' he said. ''What seals the deal for them is that he was killed by the United States.'' [...]

So, was there a better idea of how to deal with Awlaki once he had joined Al Qaeda? Yemeni tribes might have been induced to capture him and turn him over, but a criminal trial would have given a global audience to a mesmerizing orator. Martyrdom would have been avoided, but his YouTube presence would have lived on intact. A more outlandish idea was raised immediately after Awlaki's death by Ed Husain, a former British militant who recounts his journey into and out of extremism in his memoir, ''The Islamist.'' Husain suggested then, and believes now, that a better approach might have been a careful, high-profile public release of the prostitution files on Awlaki. ''He was an imam when he was up to these shenanigans,'' Husain told me. ''Exposing that, I think, would have discredited him and more important undermined the message -- that they are these high and mighty, pious, believing brothers who are declaring jihad on the West. Expose them for what they are.''

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