As my colleagues John F. Burns and Alan Cowell report, one of the two knife-wielding assailants who killed an off-duty soldier in London on Wednesday, who then calmly spoke to witnesses while waiting for the police to arrive, has been identified as Michael Adebolajo, a Briton of Nigerian heritage who converted to Islam about a decade ago.
Two former leaders of al-Muhajiroun, an extremist group with a small following that was banned in Britain after terrorist attacks in London in 2005, told reporters on Thursday that the suspect was part of their circle.
The BBC discovered footage of Mr. Adebolajo standing behind Anjem Choudary, a British co-founder of the group and its successor organizations, at an Islamist protest in London in 2007.
In another part of the video, Mr. Adebolajo, who was reportedly raised as a devout Christian by his Nigerian immigrant parents, is seen holding a sign that deplores Britain's “Crusade Against Muslims.†Mr. Choudary told Reuters that Mr. Adebolajo “used to attend a few demonstrations and activities that we used to have in the past,†but that he “would not consider him to be a member of the organization.â€
Sheik Omar Bakri Mohammed, a Syrian-born cleric who led al-Muhajiroun until he was expelled from Britain, said in an interview from Lebanon with The Independent that he recalled meeting Mr. Adebolajo. “I knew him as Michael when he came to the meetings, and then he converted and he became known as Abdullah,†he said. “I hear he then started calling himself Mujahid. He asked questions about religion; he was curious. He had first started coming when there was a lot of anger about the Iraq war and the war on terror. Whether I influenced him or not, I do not know. But he was a quiet boy, so something must have happened.â€
Sheik Omar also suggested that the killing was not an act of terrorism or a crime according to his interpretation of Islamic law. “Under Islam, this can be justified,†he told The Independent. “He was not targeting civilians. He was taking on a military man in an operation.â€
The cleric also told The Guardian that the suspect had attended al-Muhajiroun events at a community center and mosque in Woolwich, where Wednesday's deadly attack was carried out near a military barracks.
Jon Ronson, a British journalist who made a documentary about Sheik Omar's quixotic campaign to bring Britain under Shariah law in 1996, reminded readers on Thursday that he had looked more closely at al-Muhajiroun in a second film made after the terrorist attacks in London on July 7, 2005, “The Tottenham Ayatollah Revisited.â€
In an essay for The Guardian in 2005, Mr. Ronson argued that Britain might ultimately regret expelling the occasionally buffoonish Sheik Omar, given that his outlandish sermons acted as a powerful magnet for the most extreme young men in his community. “Without Omar clowning around on stage,†he said, “how is Scotland Yard going to monitor the less clownish people who sit in his audience?â€
In the introduction to his book “Them: Adventures With Extremists,†Mr. Ronson wrote that Sheik Omar had mixed feelings about how the documentaries had portrayed him as a bumbling, somewhat comic figure making the exaggerated claim that he was Osama bin Laden's “man in Londonâ€:
I telephoned Omar on the evening of his arrest. I expected to find him in a defiant mood. But he seemed a little scared. “This is so terrible,†he said. “The police say they may deport me. Why are people linking me to bin Laden? I do not know the man. I have never met him. Why do people say I am bin Laden's man in London?â€
“Because you have been calling yourself bin Laden's man in London for years,†I said.
“Oh Jon,†said Omar. “I need you more than ever now. You know I am harmless, don't you? You always said I was laughable, didn't you? Oh Jon. Why don't people believe I am just a harmless clown?â€
“I have never thought you were a harmless clown,†I said.
I telephoned Omar a a few weeks later. I asked him if I could follow him around some more, now that a conclusion to his story seemed imminent. His response was startling to me. “You portray me as a fool,†he said. “I will not let you anywhere near me ever again. You hate the Muslims.â€
As Mary Fitzgerald, a foreign correspondent for The Irish Times, reported on Twitter, Sheik Omar is now based in Lebanon, where he is fighting terrorist charges and taking part in televised debates on the conflict in Syria.
According to Ms. Fitzgerald, the cleric once told her that his group tended to attract young men who felt themselves to be “caught between cultures and identities†in multicultural Britain.
Mr. Adebolajo, the son of Nigerian immigrants, would seem to fit that description. As The Lede noted on Wednesday, at one point in his statement justifying the killing, as Mr. Adebolajo implored the British citizens in front of him to get their leaders to remove their troops from “our lands,†he seemed to stumble a bit as he used words that betrayed a certain confusion about which community he belonged to, saying: “Tell them to bring our troops back, so we can - so you can all live in peace.â€
This post has been revised to reflect the following correction:
Correction: May 24, 2013
An earlier version of this post misspelled the name of the extremist group with which Michael Adebolajo was associated. It is al-Muhajiroun, not al-Muhijaroun.
Gilles Sabrie for The New York Times 
Michael Buckner/Getty Images//Noah Kalina/Facebook, via Associated Press/Kevork Djansezian/Getty Images