Umar Farouk Abdulmutallab has been charged over the incident
A former close friend of the man accused of trying to blow up a US plane has said he believes he was radicalised after leaving the UK in 2008.
Qasim Rafiq knew suspect Umar Farouk Abdulmutallab, accused of an attempted attack on Christmas Day, for three years at University College London.
He said Nigerian-born Mr Abdulmutallab, 23, had shown no signs of violent extremism during their friendship.
He said wanted to know what had driven his former friend "down this road".
Mr Rafiq's comments come as the prime minister has said the UK will "move quickly" to enhance airport security after the "wake-up call" of the alleged failed attack.
Mr Abdulmutallab took an engineering with business finance degree at UCL between September 2005 and June 2008 and was president of its Islamic Society between 2006 and 2007.
Mr Rafiq, who preceded Mr Abdulmutallab as president, said if Mr Abdulmutallab had expressed radical views during their friendship, it would have raised question marks with him.
He added there was pressure on Islamic societies after the London 7/7 bombings, so if had he done anything unusual during his time at UCL, it would have been flagged up.
Qasim Rafiq says it was a "huge shock" for him to learn of the alleged attack
Mr Rafiq told the BBC: "When I heard the news I wasn't sure what to think. I thought could this really be the same person? The humble, the kind, the well-mannered, well-spoken individual that I knew and I was a close friend to went on to do what he did.
"If I could speak to him now I would ask him: 'What is it that drove you down this road because you were not like this when I knew you?' You were not like this when you were the president of the Islamic Society.'"
Mr Rafiq said Mr Abdulmutallab had cut off contact a month after graduation, but had said he planned to do a business course in Dubai.
He said the best documented time of Mr Abdulmutallab's life was when he had been at UCL and there must be a thorough examination into what happened after he left.
On Thursday the university rejected claims Mr Abdulmutallab had been radicalised while there as "spectacular insinuation".
Malcolm Grant, the university's provost, rejected reports the suspect had helped organise a "war on terror" conference two years ago.
Announcing a full independent review of Mr Abdulmutallab's time at UCL, he said if any evidence emerged of "a wider malign impact on him or by him, we shall certainly take appropriate action".
Meanwhile, Mr Brown said he had ordered a review of existing airport security measures, which would report within days.
Full-body scanners would be among the new technologies considered, he said.
He also said Mr Abdulmutallab had linked up with al-Qaeda in Yemen after leaving London.
Mr Abdulmutallab allegedly attempted to ignite explosives stored in his underpants. He had flown from Lagos to Amsterdam before changing planes for a flight to Detroit.
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