The BBC has learned that more than ten years prior, MI5 had suspicions about a Muslim preacher who was close to the Manchester bomber.
This week, a public investigation into the massacre will release a report on Salman Abedi's radicalization and whether security services had any opportunities to stop him.
Before a different one of his close friends attempted to carry out a suicide bombing in Exeter in 2008, the preacher Mansour Al-Anezi had been under investigation.
Al-Anezi passed away prior to the arena attack.
In the bombing, twenty two people perished. Evidence from MI5 regarding Abedi and associates who were known to the security service was discussed in closed-door hearings without the participation of the victims' families.
A BBC investigation has uncovered information that may not have been disclosed in the closed sessions or in the public hearings.
In the UK, suicide bombings—both actual and attempted—are uncommon. The Manchester and Exeter bombings were the only two confirmed incidents in the previous 15 years.
It has not been publicly acknowledged that a bombing in a taxi in Liverpool in 2021 that killed the bomb maker was an intentional suicide bombing.
It may have been a coincidence that Al-Anezi's associates were involved in both Manchester and Exeter. However, the BBC has learned that, prior to the Exeter attack, the authorities were looking into him as a possible radicalizer.
Detective Chief Superintendent Simon Barraclough, the officer in charge of the Manchester investigation, testified before the arena inquiry that there was "clearly a connection of significance" between Salman Abedi and Al-Anezi, but police were unable to pinpoint what it was.
Al-Anzei had reportedly been detained in relation to the attack in Exeter, according to the investigation. However, the public hearings were not informed of the earlier MI5 investigation.
The preacher, who was not charged, regularly oversaw prayers at a Plymouth mosque that the bomber, Nicky Reilly, a Muslim convert who was 22 at the time, frequented.
Reilly had Asperger's Syndrome and had trouble learning. His family believed he was susceptible to influence and the opinions of others.
As he was getting ready to detonate three devices, a nail-bomb partially exploded in the restroom of a busy restaurant, injuring only him.
In 2016, he passed away in custody.
On the ninth anniversary of the Exeter attack, Salman Abedi committed the bombing of the Manchester Arena.
AI-Anezi, a 43-year-old Kuwaiti national, arrived in the UK in 2000. He started out in Manchester and then moved to Plymouth.
When Al-Anezi relocated to Devon, MI5 alerted the authorities. The Plymouth mosque where he gave sermons was under surveillance, and MI5 gathered information about his whereabouts.
Al-Anezi was close to Reilly and was suspected following the incident in Exeter. Although the detectives lacked sufficient proof to charge him, they continued to look into him.
In the months following the Exeter attack, Simon Hall, a Cambridge lecturer and former BBC correspondent in south-west England, recalled seeing a surveillance operation around Al-Anezi.
Hall claims that while waiting for him at the same location in Plymouth one day, plain-clothed investigators asked him not to approach Al-Anezi.
After Reilly's conviction, Hall produced a report on Al-Anezi for television. Legal constraints prevented it from naming the preacher.
After the Exeter attack, according to two sources who managed the mosque where Al-Anezi led prayers, he was forbidden from giving sermons. One told the BBC that he was told "no politics.".
Al-Anezi acknowledged that some worshipers had expressed concerns about his views and that there had been a later immigration case.
Al-Anezi lived in Plymouth but frequently traveled to Manchester where he eventually met Salman Abedi. He stayed at the city residence of the Abedi family. Items belonged to Al-Anezi were discovered there following the bombing.
He also spoke on the phone with Hashem Abedi, who coordinated the attack with his brother Salman.
When Al-Anezi passed away in a Plymouth hospital in January 2017, Salman Abedi was by his side. Abedi was in tears, according to a second close friend of his who was in the room and told the BBC.
Al-Anezi's funeral was held in Manchester, and Salman and Hashem Abedi were there. The next day, they made a significant advancement in their bomb plot by purchasing an explosives-making chemical.
Al-Anezi may have used several aliases, and the BBC's investigation indicates that his real name may have been entirely different.
He acknowledged using a "fake passport" to enter the UK under the name Nasar Al Ajmi, according to a 2009 asylum judgment made available to the BBC, but he claimed the document was lost and he couldn't remember the airport he arrived at.
He "wanted to conceal information," according to the government, and he "fabricated his claim for asylum.".
He had claimed to be a Bedouin, a minority group in Kuwait, and had provided accounts of being persecuted. At his appeal, the judge agreed that his accounts were reliable.
However, the BBC discovered contradictions in his story.
According to the appeal judgment, Al-Anezi claimed that his parents had passed away and that "he had one brother who was lost" because he had not come home after going shopping in Kuwait.
Al-Anezi, however, left behind parents and siblings in Kuwait, according to the funeral announcement at a mosque in Manchester. One of his associates has told the BBC about how Al-Anezi set up the transfer of thousands of pounds to a brother who lived abroad after his passing. According to reports, Al-Anezi's brother revealed that he had Egyptian ancestry and went by the name Mohammed Idrisi.
Salman Abedi may have been influenced in other ways as well, including while he was a member of Manchester's Didsbury Mosque, according to the investigation.
Two additional young men who went to the mosque, according to the BBC, lost their lives in a foreign conflict. Before the bombing at the Arena, they were exalted as martyrs online.
An ex-Imam from Didsbury who has criticized those in charge of the mosque made a brief mention of one during the inquiry. Extremists, according to him, could attend.
One of the young attendees "joined ISIS and al-Qaeda" in Libya, according to the former Imam Mohamed El-Saeti, and died fighting there.
The mosque claims that it has consistently made it clear that the "barbaric" arena bombing had nothing to do with it, Islam, or the Quran. It also claims that it was intended to distract attention from the very real shortcomings of the agencies tasked with protecting the public and preventing such attacks.
The young man mentioned by Mr. El-Saeti has been praised in online posts, according to the BBC. Friends of the Abedi brothers, including another Manchester resident and former suspect in the arena attack Zuhir Nassrat, brought up Abdulla Fieturi's passing.
Nassrat told a relative, "you should be happy," and called him a "shaeed" (martyr). The relative replied that the boy "always wanted to die shaheed," adding that he was "proud" of the boy.
Despite being in Libya, Zuhir Nassrat is wanted by the police for his involvement in a drug conspiracy involving associates of the Abedi brothers.
A different young man who died abroad was not taken into account during the inquiry's public hearings, nor was his father, who knew Salman Abedi.
Taher Nasuf, his father, frequently went to the mosque in Didsbury. He spent years under United Nations sanctions for alleged ties to the Libyan Islamic Fighting Group, which was later outlawed in Britain as an al-Qaeda affiliate, so British authorities were aware of him. He refuted the claims and was never indicted for a crime. In 2011, the individual sanctions were finally lifted. The BBC tried to get in touch with him, but he did not respond.
He belonged to the Libyan 17 February Forum, a legitimate political organization that held meetings at the mosque.
Salman Abedi was captured on camera grinning while Mr. Nasuf was speaking at one of its demonstrations in London.
According to information provided to the BBC, Reda, a student at the Didsbury mosque, also lost his life in a foreign conflict. He was referred to as a martyr in online posts, including those of Mustafa Graf and another Didsbury Imam. Another picture shows him with Abdalraouf Abdallah, who was later found guilty of terrorism offenses for facilitating the flow of fighters and cash to Syria, and another one with him dressed in military garb.
The investigation looked into whether Salman Abedi was radicalized by Abdallah.
Five families who lost loved ones in the Manchester attack responded to the BBC's request for their thoughts on all of the evidence by saying they are "disappointed to learn of yet more links to terrorism in Abedi's background which do not appear to have been investigated.".
The families are those of Liam Curry, 19, and Chloe Rutherford, 17, both of South Shields; Eilidh MacLeod, 14, of Barra; Megan Hurley, 15, of Liverpool; and Kelly Brewster, 32, of Sheffield.
In a statement to the BBC, they said, "We would have expected the government to do the same and investigate fully if there is enough information in the public domain for the press to make these links.".
The families state: "We can only hope that this information was covered in the public inquiry's closed hearings. ".
Given how much the MI5 knew about the Abedi family, they are critical of the agency.
"Our thoughts remain with those who were killed or had their lives forever changed at the Manchester Arena attack," a spokesman for the Home Office said.