Investigators on both sides of the Atlantic were last night urgently investigating the background of the would-be plane bomber, as international attention turned to al-Qaida's stronghold in Yemen.
Scotland Yard and MI5 want to establish how Umar Farouk Abdulmutallab was radicalised and by whom, and whether he had accomplices in the UK or the Arabian peninsula. He has told US officials that he met al-Qaida operatives in Yemen who gave him the device which almost brought down Northwest Airlines flight 253 to Detroit and taught him how to use it.
Yesterday it emerged that after attending university in London, the 23-year-old had dropped out of a postgraduate business course in Dubai, telling his family he had gone to Yemen to study Islam. He then cut off contact with them.
Repercussions from the failed Christmas Day plot continued yesterday, with Barack Obama ordering a review of US security as politicians demanded to know how the British-educated Nigerian was able to get on the plane after his father, a wealthy banker, had been concerned enough to warn US diplomats that his son might be a security risk.
Obama's spokesman said he was seeking answers to why Abdulmutallab was placed on the least urgent of three US watchlists of possible terrorism suspects, rather than a higher category which would have prevented him flying.
Robert Gibbs told ABC News: "The president has asked that a review be undertaken to ensure that any information gets to where it needs to go, to the people making the decisions. The president wants to review some of these procedures and see if they need to be updated."
Passengers on transatlantic flights faced delays of several hours at the weekend as extra security checks were rushed through, with people heading for the US being frisked and having hand luggage searched. Some reported having Christmas presents unwrapped.
The heightened state of security was underlined last night when the crew of another Amsterdam to Detroit flight, with the same flight number, reported an emergency incident after an "unruly" Nigerian man raised concerns by spending an unusually long time in the plane's bathroom. He was detained by the FBI after the plane landed, but turned out to have a "legitimate illness," officials from the department of homeland security said.
Some new details about Abdulmutallab became clear yesterday.
• Whitehall officials confirmed that in May they had turned down his application to return to the UK to study, although this was because his chosen college was considered a bogus institution, rather than due to fears that he might be a terrorist. • They said he did not come to MI5's attention during his three years studying engineering at University College London, though police were continuing yesterday to search his luxury apartment in a central London mansion block.
• Abdulmutallab's father, a former government minister who recently retired as chairman of the First Bank group in Nigeria, was yesterday still speaking to investigators. He had been so concerned at his son's views that several months ago he reported his fears to the Nigerian security services and the US embassy.
• Al-Qaida activists in Yemen referred in a video recorded on 21 December to "a bomb to hit the enemies of God". It was not known if this was a general warning, or indicated a clear Yemeni link.
Abdulmutalab, who has been charged with trying to blow up the Northwest Airlines plane, was transferred to a federal prison near Detroit, his lawyer said.
In the US, Joe Lieberman, chairman of the Senate's homeland security committee, said he believed that the fact Abdulmutallab was even allowed to board a flight from Lagos to the US, via Amsterdam, amounted to an intelligence failure.
"I am troubled by several aspects of this case, including how the suspect escaped the attention of the state department and law enforcers when his father apparently reported concerns about his son's extremist behaviour to the US embassy in Nigeria, how the suspect managed to retain a US visa after such complaints, and why he was not recognised as someone who reportedly was named in the terrorist database," he said. The Republican leader in the Senate, Mitch McConnell, said: "How does a person on a terrorism watchlist get a US visa? It's amazing to me that an individual like this, who's sending out so many signals, could end up getting on a plane going to the US."
The homeland security secretary, Janet Napolitano, said that while Abdulmutallab was on a general watchlist, there had not been sufficient information to move him to a much shorter list of those barred from flying. "The issue [is], was there enough information to move him to the more specific list which would require additional examination, or indeed being on no-fly status?" she said.
"You need information that is specific and credible if you're going to bar someone from air travel. He was on a general list of over half a million people, but there was not the kind of credible information that would move him up that list. Now one of the things we'll be doing is looking at those watchlist procedures."
Napolitano said there was no indication that Abdulmutallab was "part of anything larger" in terms of impending attacks.
More details emerged yesterday about the apparent radicalisation of a young man born into privilege in the Muslim-dominated north of Nigeria. He attended an elite British-curriculum boarding school in the capital of Togo, Lomé.
A former teacher of his recalled the then-teenager expressing sympathy for the Taliban after the September 11 attacks in 2001.
However, a friend from that time, James Ticknell, told the Guardian that, while Abdulmutallab had been a devout Muslim, he was not in the least militant. "He was very decent and gentle, in fact a pacifist. His views on religion were very mainstream. When I realised the man on the plane was him, I felt disbelief."
Nigeria's civil aviation authority said last night that he bought his round-trip ticket from Lagos to Detroit via Amsterdam at a KLM office in Ghana's capital, Accra, on 16 December, with a planned return of 8 January. He paid the £1,775 fare in cash. Before the flight departed on Thursday, he checked in as normal, taking only a carry-on bag.
Security at Lagos had been found adequate by US authorities. Under EU rules, Abdulmutallab would have been checked again as a transfer passenger at Amsterdam's Schiphol airport. Dutch officials say these checks took place and were "well performed".
Aviation security experts said that scanners designed to pick up explosives rather than metal exist, but are not in widespread use.
The transport secretary, Lord Adonis, said last night that he wanted to thank air passengers for their patience. "I am sure they will understand the extra precautions are being taken for their own protection," he added.
Abdulmutallab is being treated in hospital for serious burns to his leg. He is due to make his first formal court appearance in Michigan this afternoon local time.
