A British-born man suspected of masterminding Boko Haram bomb attacks in Nigeria that left around 100 people dead became radicalised during his years at a Welsh university, it has been claimed.

Aminu Sadiq Ogwuche is believed to have led a double life in the UK as an aspiring businessman while preparing to die in the name of Allah. Ogwuche, who allegedly called himself the “Lion of God” and wrote increasingly extreme posts on social media during his later years in Britain, was arrested in Sudan this week on suspicion of organising the double blast.

Experts warned that his case could signal the start of a new wave of British-Nigerian extremists travelling to fight for Boko Haram, attracted by its global notoriety following the kidnapping of more than 270 girls.

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The Nigerian authorities are now seeking the extradition of Ogwuche for the bombings of a poor suburb of Abuja, which is home to people displaced by the government’s war against Boko Haram in the north of the country.

Ogwuche had previously been detained by authorities in Nigeria on his return to the country from the UK following a reported tip-off from British intelligence, but he was released after a campaign by human rights groups and his family.

He then fled across the border but was implicated in the double bombing in Abuja. The first blast took place on the same day that the schoolgirls were seized by Boko Haram fighters in Chibok, in the north-east of the country. He was only arrested this week after a chance spotting by a former classmate from his Nigerian military school who was in Sudan with a Nigerian military delegation, according to a source. Ogwuche is a former lance corporal in Nigerian military intelligence who reportedly deserted in 2006.

Former classmates in Wales spoke of their shock that Ogwuche had been alleged to be a terrorist mastermind after spending three years studying for a degree in business science at the University of Glamorgan – now the University of South Wales – from 2007 to 2010.

Ogwuche told fellow students that he used to be in the military back “home” in Nigeria and that his goal was to become a successful businessman. However, he failed to finish the course.

A former housemate told Wales Online that he had been serious but showed no signs of potential violent extremism. Anju Moro said: “He was very devout but then many people are. He would often just spend time in his room between going to and from prayers but he seemed harmless, if very serious. It is very creepy that he could have been having thoughts like that.”

During his time in Britain in 2010, his Facebook pages included comments expressing his willingness to die. The following year it read: “The only punishment of those who wage war against Allah and His Messenger and strive to make mischief in the land is that they should be murdered, or crucified, or their hands and their feet should be cut off, or they should be imprisoned.”

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A spokeswoman for the University of South Wales said that there was “no evidence of any radical behaviour” while he was at the university.

“The university has a strong community ethos with no history or evidence of extremist behaviour across any of its campuses so it is surprised to hear of his apparent involvement with terrorist group Boko Haram,” it said in a statement. “There were no reported indications of extremist behaviour during his time as a student. There has been no contact between Ogwuche and the university following his departure in 2010.”

Ogwuche, the son of a retired army colonel, had recently been learning Arabic at the International University of Africa, in Sudan, according to reports from Africa.

Boko Haram, which roughly translates as “Western education is sinful”, wants Nigeria to be an Islamic state and has been killing innocent civilians in increasing numbers. Thousands have been killed by the group in the past five years, with more than 1,500 civilians dying in the insurgency this year alone.

An expert in extremism told The Independent that it was possible that more British-Nigerian extremists would now travel to the African country to fight on behalf of Boko Haram. A previous Nigerian extremist who was educated in Britain, Umar Farouk Abdulmutallab, trained in Yemen with al-Qa’ida in the Arabian Peninsula before trying to blow up a transatlantic flight on Christmas Day in 2009.

“It’s a surprise it has taken this long really,” said Robin Simcox, of the Henry Jackson Society. “Boko Haram is an increasingly powerful group but it hasn’t been as notorious as a group like al-Shabaab or al-Qa’ida in Pakistan or Afghanistan. It has not been a well-known group that has been able to attract Westerners.

“With Boko Haram getting increased publicity with kidnapping, maybe that will draw more to Nigeria than to the Yemen.”

Foreign Office officials said they did not believe Ogwuche was a British national. The Home Office did not deny he was British-born, but said it would not comment on individual cases.