Washington- In a series of conversations in Qaeda safe houses in Yemen in 2009, Anwar al-Awlaki carefully sized up a young Nigerian volunteer, decided the man had the diligence and dedication for a “martyrdom mission” and finally unveiled what he had in mind.

Mr. Awlaki, an American-born cleric who had become a leading propagandist for Al Qaeda, told the man, Umar Farouk Abdulmutallab, that “the attack should occur on board a U.S. airliner,” according to the account Mr. Abdulmutallab gave the Federal Bureau of Investigation.

Mr. Abdulmutallab told F.B.I. agents that he “was resolved to killing innocent people and considered them to be ‘collateral damage.’” With “guidance” from Mr. Awlaki, he said, he had “worked through all these issues.”

Newly released documents, obtained by The New York Times after a two-year legal battle under the Freedom of Information Act, fill in the details of a central episode in the American conflict with Al Qaeda: Mr. Abdulmutallab’s recruitment by Mr. Awlaki and his failed attempt to blow up an airliner approaching Detroit on Christmas in 2009 using sophisticated explosives hidden in his underwear.

The documents’ detailed account of Mr. Awlaki, who stars in Mr. Abdulmutallab’s story as both a religious hero and a practical adviser on carrying out mayhem, is particularly important. The government allegation that Mr. Awlaki was behind the underwear bomb plot — never tested in a court of law — became the central justification that President Barack Obama cited for ordering the cleric’s killing in a drone strike in Yemen in 2011.

Mr. Awlaki became the first American citizen deliberately killed on the order of a president, without criminal charges or trial, since the Civil War. Some legal scholars questioned whether the order was constitutional. Mr. Obama argued that killing Mr. Awlaki was the equivalent of a justified police shooting of a gunman who was threatening civilians.

The F.B.I.’s decision in 2010 to keep the interview summaries secret led some critics to question the quality of the evidence against Mr. Awlaki. The 200 pages of redacted documents released to The Times this week, on the order of a federal judge, suggest that the Obama administration had ample firsthand testimony from Mr. Abdulmutallab that the cleric oversaw his training and conceived the plot.

The detailed reports of Mr. Abdulmutallab may also play into the debate President Trump has renewed about whether torture is ever necessary to get useful information from terrorism suspects. Most experienced interrogators say no, and their arguments would receive support from these interviews.

The F.B.I. flew Mr. Abdulmutallab’s relatives to the United States to boost his spirits and encourage him to talk — with great success. In interview after interview, he described every person he said he could recall from Al Qaeda in the Arabian Peninsula, the branch in Yemen; discussed candidly his evolving views about carrying out a terrorist act; and tried to reconstruct the layout of a training camp, Mr. Awlaki’s house and many other Qaeda buildings. His descriptions were so precise that it is likely they have helped shape targeting decisions in the American drone campaign in Yemen.

Mr. Awlaki, whom everyone at the Qaeda training camp called “sheikh” out of respect for him as a religious leader, spoke at length with the Nigerian, then 23 and the son of a wealthy banker, about what he saw as the religious obligation of jihad. He put the younger man up at his house in the province of Shabwah, where Al Qaeda had a large presence, and introduced him to other Qaeda trainers and bomb makers, Mr. Abdulmutallab told the F.B.I.

Mr. Awlaki helped Mr. Abdulmutallab prepare a martyrdom video, telling him to “keep it short and reference the Quran.” He gave the recruit a way of staying in touch, evidently an email address, to report on the proceedings.
He advised Mr. Abdulmutallab to blur his trail by traveling from Yemen to an African country before booking the flight on which he intended to detonate his bomb. The choices of exact destination and timing were left up to Mr. Abdulmutallab, who said Detroit and Dec. 25 were random decisions dictated by ticket prices and flight schedules.
Mr. Awlaki offered a final reminder: “Wait until you are in the U.S., then bring the plane down.”

With this instruction in mind, Mr. Abdulmutallab told the F.B.I., he followed the progress of Northwest Airlines Flight 253 on the seat-back screen from Amsterdam into Canada, then waited as it approached the United States border. He went to the airliner’s bathroom to make final preparations for his attack and considered trying to set off the bomb there. But to be certain he was over American soil, he returned to his seat to check the map before pushing the plunger under his clothing to mix the chemicals and ignite the explosives.

Perhaps because of excess moisture, the contraption did not explode but let out a flame, seriously burning Mr. Abdulmutallab, who said he tried to get his burning pants off before passengers jumped on him. One crew member threatened to throw him out of the plane, and a passenger hit him once before another crew member intervened, he said.

Mr. Abdulmutallab began speaking to officials before leaving the plane, admitting that he had tried to set off a bomb and that he was a member of Al Qaeda. He later stopped talking, but resumed within a few weeks and appears to have become completely cooperative. He surprised prosecutors at his 2011 trial by suddenly insisting on pleading guilty, and he was sentenced to life in prison in 2012.

In 2005, he discovered the recorded lectures of Mr. Awlaki — who had not yet fully embraced violence — on sale in a bookstore in London. In 2009, while living in Dubai, in the United Arab Emirates, he came to feel that “God was guiding him to jihad,” and he set out to Yemen to try to find the American cleric, by then a rising Qaeda leader.

In training, he fired a Kalashnikov rifle a few times but was “never comfortable” shooting. However, Mr. Awlaki was persuaded that he could be trusted with a suicide attack. When a friend from Nigeria called to urge Mr. Abdulmutallab to come home, he realized his parents were behind the call. He agonized, as he prepared for the flight to Detroit, about how to tell them goodbye.

He told the F.B.I. agents that only Mr. Awlaki or a comparable figure, not his parents, would have “the religious authority” to dissuade him from carrying out the attack. His last email from Mr. Awlaki offered encouragement for his lethal mission. “I wish it all goes well, I wish you the best,” the cleric wrote.

New York Times