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.
His F.B.I. interviews amount to a sort of jihadist bildungsroman, telling the story of a shy, serious and earnest son of a prominent Nigerian businessman. He attended University College London, hoping to study engineering and go to work for his father’s construction company, he told the F.B.I. He lived with his brother in an expensive apartment his family owned in the British capital.
But he became interested in religion, and it gradually took over his life. In 2005, he discovered the recorded lectures of Mr. Awlaki — who had not yet fully embraced violence — on sale in an Islamic 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. His sober devotion to the jihadist cause, however, persuaded Mr. Awlaki 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 jihad. 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.
When the agents asked whether, in retrospect, Mr. Awlaki’s documented patronage of prostitutes disturbed him, he demurred. It might be false slander, he said. If not, then Mr. Awlaki “could repent for those sins and his commitment to jihad would outweigh such transgressions,” Mr. Abdulmutallab said.
The Abdulmutallab interviews were initially sought from the F.B.I. for a 2015 book about the life and death of the cleric. The Times subsequently sued to obtain the documents, which the F.B.I. said should be secret to protect terrorism investigations.
In December, Ronnie Abrams, a federal judge in Manhattan, ordered the bureau to conduct a “line-by-line” review and to hand over whatever could be safely released. The 200 pages made available have the names of Qaeda operatives and other details redacted but give a rare firsthand account of the evolution of a terrorist who survived his suicide mission.