Manchester, England (CNN) Salman Abedi, the man who carried out the deadliest terror attack to hit the UK in 12 years , grew up in Manchester with parents who had fled Libya under Moammar Gadhafi.

Abedi's father returned to the African nation in 2011 after the rebels overthrew the government and his wife joined him earlier this year.

After getting word that Salman Abedi and his brother Hashim were getting into trouble in England, Ramadan Abedi sent for his boys and they joined their parents about a month ago, a family friend in Libya told CNN.

But Salman Abedi came back to England last week after telling his father he wanted to make a pilgrimage to Saudi Arabia, the source -- who asked not to be named for discussing sensitive family matters -- and a source in the Libyan community of Manchester, told CNN.

Three days after he returned, Salman Abedi went to an Ariana Grande concert where authorities said he detonated a bomb that killed 22 fans -- many of them children and young people -- who were leaving the Manchester Arena. Scores more people were hurt, some critically.

Abedi, 22, is believed to have died in the powerful blast, but a coroner has yet to officially identify his remains, Manchester police said.

On the radar

Abedi was already known to authorities, UK Home Secretary Amber Rudd said Wednesday. But it's not yet clear why he was on their radar.

Rudd said authorities were aware of him, to a point. "The intelligence services know a lot of people, and I'm sure we will find out more what level they knew about him in due course," she told the BBC.

"But at the moment all they have confirmed is that they did know about him, and as I say we will find out more when the operation is complete."

Salman Abedi in a Facebook image from a few years ago.

Authorities now are working to track down Salman Abedi's associates.

"It is very clear that this is a network we are investigating," Greater Manchester Police Chief Constable Ian Hopkins said Wednesday.

Rudd had earlier told the BBC that the bomber may not have worked alone.

Photos: Deadly explosion at Ariana Grande concert People in Manchester, England, gather in St. Ann's Square on Thursday, May 25. They were observing a national minute of silence to remember the victims of a suicide bombing at an Ariana Grande concert. Hide Caption 1 of 22 Photos: Deadly explosion at Ariana Grande concert Britain's Queen Elizabeth II speaks to 15-year-old Millie Robson and her mother, Marie, during a visit to the Royal Manchester Children's Hospital on May 25. The Queen was visiting those injured in the attack. Hide Caption 2 of 22 Photos: Deadly explosion at Ariana Grande concert A police officer guards a house in Manchester as investigations continued on May 25. Police say a man carrying explosives acted as a lone attacker and died in the blast. Hide Caption 3 of 22 Photos: Deadly explosion at Ariana Grande concert Flowers and tribute messages are left for victims in St. Ann's Square. Hide Caption 4 of 22 Photos: Deadly explosion at Ariana Grande concert A women sheds tears after observing the minute of silence in St. Ann's Square. Hide Caption 5 of 22 Photos: Deadly explosion at Ariana Grande concert A Manchester road is closed off as police raids continued on May 25. Hide Caption 6 of 22 Photos: Deadly explosion at Ariana Grande concert Local residents hold Manchester City and Manchester United soccer jerseys during the national minute of silence. Hide Caption 7 of 22 Photos: Deadly explosion at Ariana Grande concert Police officers deliver flowers to a makeshift memorial in Manchester on Wednesday, May 24. Hide Caption 8 of 22 Photos: Deadly explosion at Ariana Grande concert Women cry after placing flowers in Manchester on May 24. Hide Caption 9 of 22 Photos: Deadly explosion at Ariana Grande concert A forensics team works at the scene of the explosion on Tuesday, May 23. Hide Caption 10 of 22 Photos: Deadly explosion at Ariana Grande concert British Prime Minister Theresa May condemns the "callous terrorist attack" as she delivers a statement in London on May 23. Hide Caption 11 of 22 Photos: Deadly explosion at Ariana Grande concert Police help someone after the attack at Manchester Arena on Monday, May 22. Hide Caption 12 of 22 Photos: Deadly explosion at Ariana Grande concert People gather outside the arena. "We can confirm there was an incident as people were leaving the Ariana Grande show last night," police said on Twitter early on Tuesday. "The incident took place outside the venue in a public space. Our thoughts and prayers go out to the victims." Hide Caption 13 of 22 Photos: Deadly explosion at Ariana Grande concert People receive medical attention at a railway station close to the arena. The incident happened shortly after Grande had left the stage, shortly after 10:30 p.m. (5:30 p.m. ET) according to eyewitnesses. Calvin Welsford, an 18-year-old concertgoer, said that he heard a "loud bang" a couple of minutes after Grande's set had finished. Hide Caption 14 of 22 Photos: Deadly explosion at Ariana Grande concert Paramedics respond to the scene. Hide Caption 15 of 22 Photos: Deadly explosion at Ariana Grande concert Emergency workers and concert attendees gather outside the arena. Hide Caption 16 of 22 Photos: Deadly explosion at Ariana Grande concert People stand by a cordoned-off street close to the arena. Hide Caption 17 of 22 Photos: Deadly explosion at Ariana Grande concert Greater Manchester Police tweeted that emergency services were "responding to (a) serious incident at Manchester Arena. Avoid the area. More details will follow as soon as available." Hide Caption 18 of 22 Photos: Deadly explosion at Ariana Grande concert People are escorted away from the arena. Hide Caption 19 of 22 Photos: Deadly explosion at Ariana Grande concert People sit outside near the arena. The crowd was made up of mainly younger people who had come to see Grande in her first of three scheduled concerts in the UK. Hide Caption 20 of 22 Photos: Deadly explosion at Ariana Grande concert An injured man is helped at the scene. Hide Caption 21 of 22 Photos: Deadly explosion at Ariana Grande concert People hug near armed police who responded to the scene. Hide Caption 22 of 22

The motive for carrying out the attack remained unknown on Wednesday morning. ISIS claimed responsibility, saying Abedi was a "soldier of the caliphate," but offered no evidence.

French Interior Minister Gérard Collomb told BFM-TV that Abedi had "proven links to ISIS," though he did not elaborate. Rudd declined to comment on the claim.

Time in Libya

The Abedi family friend told CNN the two brothers wanted revenge for a friend who was killed by a gang.

Their father, a police officer in Libya, got them to go there and took away their passports.

Salman Abedi got his travel documents back by saying he wanted to make an Umrah, or pilgrimage, to Mecca, the friend told CNN.

US military officials assigned to Africa Command told CNN that Salman Abedi had been in Libya for three weeks

That specific information has been shared between US and British intelligence services, the US officials said, adding they currently have "high confidence" the information is accurate.

The trip raises questions about what he was doing there, whom he met with and whether he received training or support.

Abedi was a student at the University of Salford -- Manchester's third largest university -- where he studied business and management in the 2015-2016 academic year. He was enrolled for a second year, but hadn't been attending classes, nor had he been active in school life, according to those who knew him.

Abedi did not stay on campus in Salford, instead living in the Fallowfield area of south Manchester.

Suspected bomber was lonely child

Details are slowly emerging about Abedi, who was born and raised in the United Kingdom, according to Prime Minister Theresa May.

Abedi had seemed like a lonely child, who kept himself to himself, according to long-time family friend Akram Ben Ramadan, a British Libyan who had known Abedi and his brother, Ismael, since the Abedis were children. There were four children in the family in total -- three boys and one girl.

Abedi went to a Manchester school, Burnage Academy for Boys, from 2009 to 2011. The school declined to comment on his time there but sent a message of support to all those affected by the attack.

Ramadan, who had not seen Abedi much in recent years, said he had noticed that he had begun to dress "Islamically," in a long robe, and was growing a beard.

The Manchester Islamic Centre and Didsbury Mosque, a couple of miles from Abedi's home, condemned the "horrific" bombing in a statement on its website Wednesday.

And Fawzi Haffar, a trustee of the center, told reporters gathered outside the large, red brick mosque -- which welcomes thousands of Muslims every week -- that a small number of media reports that claimed the bomber had worked at the site were "not true."

Monday's attack "shocked us all," he said. "This act of cowardice has no place in our religion or any other religion for that matter. We encourage anyone, and I repeat anyone, who may have information about the individual involved to contact the police without any delay."