Salman Abedi was reported to authorities for his extremist views, yet he managed to walk into Manchester Arena and detonate a suicide bomb, killing 22 people.

The British-born son of Libyan parents, he was banned from a mosque in the city, after criticising an imam for “talking bollocks” during a sermon criticising the Islamic State (IS) terror group.

A number of people who knew him, and even family members, had reportedly warned authorities he was developing radical views - including, the BBC said, that being a suicide bomber was okay - prompting concerns that signs of the threat he posed were missed.

College students were among those who raised ‘concerns’ about Abedi years ago.

A source at South Trafford College, in Altrincham, said authorities may have missed opportunities to follow up on the concerns, which were raised at least two years prior to the attack.

The anonymous source told the M.E.N: “The attacker spent two years at Trafford College before going to university. Concerns were raised about him by fellow students at the time. I’m not sure this was followed up.”

But bosses at the college said there was no ‘flag’ against Abedi’s name on college records which would indicate any cause for concern.

The college confirmed that Abedi joined in 2013 to study Business before leaving to further his studies at Salford University.

The 22-year-old’s father, Ramadan, and brother, Hashim, have been detained in Libya and another brother, Ismail, was arrested in Manchester on Tuesday.

In an interview before his arrest, Ramadan Abedi rejected claims he was a member of the Libyan Islamic Fighting Group, but added that he supports the organisation, which is banned in the UK.

In the translated interview, shown on BBC, he said: “I condemn anyone who says I belong to Libyan Islamic Fighting Group.

“I commend them but I don’t belong to any organisation.”

While Abedi was born and raised in Manchester, his parents had arrived in the UK having fled the Gaddafi regime in Libya in the early 1990s.

How he went from being a typical Mancunian schoolboy to a mass murderer seemingly linked to IS will be one of the major questions of the investigation.

Protesting his son’s innocence with regard to the Manchester Arena explosion , Ramadan Abedi added: “I’m sure that Salman didn’t carry out such an act.”

The French interior minister said Abedi had “most likely” been in Syria, another claim his father dismissed, saying he had checked his son’s passport.

While Mr Abedi said his son had seemed “normal” when he spoke to him five days before the atrocity, Jamal Zubia, a member of the large Libyan community in Manchester, told the Times the parents were so concerned about their son’s apparent descent into extremism that they took his passport.

He said: “The father had all the passports with him and was holding them.”

But Abedi convinced them to return it, claiming he wanted to make a pilgrimage to Mecca , Mr Zubia said.

It's reported he in fact came back to the UK, via Germany, from Turkey four days before the bombing.

A German magazine reported that he came through Dusseldorf, and said he had not been on any international watch list.

Home Secretary Amber Rudd confirmed Abedi had recently returned from a visit to Libya, and said the nature of the attack suggested he may have had support.

Akram Ramadan, 49, part of the close-knit Libyan community in south Manchester, said Hashim, who he described as “the little boy”, had lived in Germany.

(Image: Force for Deterrence in Libya/PA)

Mr Ramadan, who lived in the flat above Ismail, said of the incident when Abedi was banned from Didsbury Mosque: “There was a sermon about anti-Daesh (IS) and he stood up and started calling the Imam - ‘You are talking bollocks.’

“And he gave a good stare, a threatening stare into the Imam’s eyes.

“He was banned.”

Of Abedi’s motives for the attack Mr Ramadan said: “Something flipped him. Brain-washed, seen something, heard something. It is unbelievable.”

Abedi was previously a student at Burnage Academy for Boys and Manchester College, and had studied at Salford University but dropped out before finishing.

He was registered as living at Elsmore Road as recently as last year, where police raided a property on Tuesday.

Neighbours recalled an abrasive, tall, skinny young man who was little known in the neighbourhood, and often seen in traditional Islamic clothing.

He's thought to have lived at a number of addresses in the area, including one in Wilbraham Road, where plain-clothes police made an arrest on Tuesday.

A family friend, who asked not to be named, said they were known to the Libyan community in the city and described Abedi as “normal”.

A city centre flat was raided on Wednesday. A nearby bar owner said officers told him they believed Abedi had been in the flat before he carried out the bombing.

Just 15 minutes before he blew himself up, Abedi called his mother and brother, a spokesman for the Libyan government told the Times.

They claimed Hashim admitted, under interrogation, that he was aware of his brother’s plans.