The business school dropout who committed mass murder at a pop concert in Manchester had developed "an attitude problem and started chanting" over the past year, neighbours say.
With troops being deployed across Britain as the nation's terror threat level raises to critical, details about Salman Abedi's spiral into radicalism have begun to emerge from neighbours whose street became the site of a major police operation as they swooped on the suspect's home.
Investigators are still trying to determine whether the bomber was working alone or if he had connections to a wider terrorist cell.
Police arrested one 23-year-old in the raids, thought to be Abedi's brother Ismail Abedi, who the Press Association reports was born in Westminster in 1993.
The 22-year-old suicide bomber suspect was born in Manchester to Libyan parents who fled to England to escape the Gadhafi regime.
A childhood friend of Ismail, who asked not to be named, described Abedi as a "normal" child from a family known among Manchester's Libyan diaspora.
"Ismail's brother was kind of like a normal guy," he told the Press Association.
"He was always friendly, nothing to suggest (he was violent). He was normal, to be honest."
Abedi was studying business management at Manchester's Salford University before dropping out and starting down the path of radical Islamism two or three years ago, the Press Association reports.
British police and intelligence services are now investigating whether the football-obsessed Abedi had made trips via train into Syria to engage in Islamic State militant training.
Neighbours in the Manchester suburb of Fallowfield said Abedi had recently gone through noticeable change, one suggesting to The Sun he "he had an attitude problem".
"A couple of months ago he [Salman] was chanting the first kalma [Islamic prayer] really loudly in the street. He was chanting in Arabic," neighbour Lina Ahmed said.
"He was saying 'There is only one God and the prophet Mohammed is his messenger'."
It is thought Abedi might have a younger brother named as Hashim Abedi, as well as a sister named Jomana, whose Facebook profile suggests she lives in Manchester but is from Tripoli.
Members of Manchester's Islamic community have said some of Abedi's family may have returned to Libya in recent years.
A US government source said investigators were looking at whether Abedi had travelled to Libya and whether he had been in touch with Islamic State militants there.
Abdalla Yousef, a spokesman for the Didsbury Mosque in Manchester, said Abedi's father and brother had prayed there but Abedi had worshipped at another mosque.
"I have managed to track down somebody who knows the family. He confirmed his father and sister and the rest of the family had moved [back] to Libya and had moved there straight after the revolution, after Gadaffi was killed," Yousef said.
Businessman and trustee of the mosque Fawaz Haffar told the Evening Standard Adebi's brother attended prayers and volunteered at the mosque until recently and the bombing suspect "probably" attended prayers among the 1000 worshippers.
"I came earlier to ask any of the employees whether they knew him, people said they don't know him," he said about the bombing suspect.
"We make sure they preach the true Islam, the modern Islam, that preaches love to each other, peace and harmony.
"We did not want to end up with a radical mosque like what has happened in other parts of the UK."
In the raids on Tuesday police removed numerous items including what appeared to be a small reference book with "Know Your Chemicals" on the cover.
Several children are among the dead from Monday night's shrapnel bombing at the Manchester Arena that killed 22 people, left 59 hospitalised and a further 60 treated at the scene.
British Prime Minister Theresa May called it an act of "sickening cowardice" targeting "defenceless children and young people", placing it among "the worst terrorist incidents" in the country's history.
"A single terrorist detonated his improvised explosive device near one of the exits of the venue, deliberately choosing the time and place to cause maximum carnage and to kill and injure indiscriminately,” she said outside 10 Downing Street, London.
"It is now beyond doubt that the people of Manchester and of this country have fallen victim to a callous terrorist attack, an attack that targeted some of the youngest people in our society with cold calculation.
"The cowardice of the attacker met the bravery of the emergency services and the people of Manchester.
"Let us remember those who died and let us celebrate those who helped safe in the knowledge that the terrorists will never win and our values, our country and our way of life will always prevail."
The Islamic State has claimed responsibility for the attack that killed several children and adults including eight-year-old schoolgirl Saffie Roussos.