He was a devout young man, the quiet and studious son of a wealthy Nigerian banker. But long before his arrest for a dramatic attempt to blow up a U.S. passenger jet, the danger signs were already visible, a neighbour says.
Umar Farouk Abdulmutallab, accused of trying to trigger a bomb on Northwest Airlines flight 253 as it approached Detroit on Christmas Day, resembled at first glance any other young man in the northern Nigerian city of Kaduna. He wore designer clothes, sunglasses and fashionable suits.
But his neighbour, a human-rights activist named Shehu Sani, noticed that he stayed at the mosque far longer than anyone else after prayers. He rarely talked to the other young men of the city, and his conversations, when he did talk, were mainly about Islam.
In a region of Africa where militant forms of Islam were gaining momentum, his decision to study in the radical hotbed of Yemen was far from unusual. And when the 23-year-old man was charged with the attempted bombing of the U.S. airplane on Friday, his neighbour was not shocked or surprised.
"The only place you would see him, aside from his house, was the mosque," Mr. Sani said in a telephone interview from Kaduna, where he lives just two doors down the street from Mr. Abdulmutallab's main family home.
"There is a serious and growing problem of Islamic fundamentalism in this part of Nigeria. Young people are getting very aggressive and intolerant. Hundreds of young men from this part of the country are currently studying in the Middle East. He is a product of this type of hatred and intolerance."
Mr. Abdulmutallab had enjoyed an elite education, studying at the British International School in the West African country of Togo and later enrolling at University College London to study engineering and business finance. His father had several homes, including an apartment in London.
But reports said he had defended the Taliban in discussions in 2001, was isolated from other students in London and had become estranged from his family several months ago.
His father, prominent banker Alhaji Umar Mutallab, was worried by the signs of radicalization in his son. He contacted the U.S. embassy in Nigeria to report his concerns.
Nigeria is one of a growing number of African countries where Islamic militancy has taken hold, providing a new source of recruits for radical groups such as al-Qaeda.
When a militant group linked to al-Qaeda kidnapped Canadian diplomats Robert Fowler and Louis Guay last year in Niger, across the border from northern Nigeria, an intermediary who negotiated with the group noticed that one of its members was a Nigerian. Other members of the kidnapping group came from across West Africa, he said.
Militants linked to al-Qaeda have also been active in a wave of terrorist attacks in remote Saharan regions of Algeria, Mali and Mauritania. As recently as this month, the group known as al-Qaeda in the Islamic Maghreb - the same group responsible for abducting the two Canadian diplomats last year - was reported to have kidnapped three Spaniards, two Italians and a Frenchman in Mali and Mauritania.
In the war-torn nation of Somalia, the main rebel group has close connections to al-Qaeda, according to Western intelligence agencies, and has increasingly resorted to suicide bombings and other tactics associated with al-Qaeda. Foreign fighters linked to al-Qaeda have reportedly moved to Somalia, bringing with them suicide bombing.
Nigeria, the most populous country in Africa, has long been a target for al-Qaeda's efforts. The group's leader, Osama bin Laden, issued a recording in 2003 that declared Nigeria to be "ripe for liberation." He called on the country's 70 million Muslims to rise up against the Nigerian government, which he denounced as "slaves to America."
The vast majority of Nigeria's Muslims are moderates with little interest in radical Islamic ideologies. But in 2007, police arrested several alleged terrorists in Nigeria's predominantly Muslim northern states, accusing them of having links to al-Qaeda and planning to carry out attacks with explosives.
Thousands of people have died in clashes between Muslims and Christians over the past decade in Nigeria, especially when the northern states adopted the sharia system of Islamic courts.
The northern city of Funtua, the hometown of Mr. Mutallab, became the focus of international outrage in 2002 when its sharia court sentenced a woman to death by stoning for adultery. The sentence was later overturned by an appeal court.
Just five months ago, hundreds of people were killed in the northern Nigerian city of Maiduguri when security forces clashed with a radical Islamic sect known as Boko Haram, which was seeking a wider adoption of sharia law.
Mr. Sani, the human-rights activist, wrote a satirical play about sharia law in 2007, but it was banned by a sharia court in Kaduna.
"This has always been the trend, and the violence was simply a matter of time," Mr. Sani said. "This is a city with a history of religious intolerance and extremism. It's a major security problem in northern Nigeria."
Geoffrey York