Manchester Arena bomber Salman Abedi was brought to M15's attention at least 18 times before the 2017 terrorist attack, a public inquiry has heard.
The security services received their first notice of him in 2010 and he was made a “subject of interest” in 2014, but the file was deleted four months later.
Abedi has also been identified in connection with six different MI5 topics of interest, twice visited a terrorist in prisons, and traveled regularly to war-torn Libya, a public inquiry heard.
Abedi intelligence came to MI5 for six years and up until the months before it blew itself up with a homemade bomb full of splinters and murdered 22 spectators in the Manchester Arena foyer at the end of an Ariana Grande concert.
Manchester Arena bomber Salman Abedi was brought to M15's attention at least 18 times before the 2017 terrorist attack, a public inquiry has heard
Abedi intelligence came to MI5 for six years and up to the months before it blew itself up with a homemade bomb full of shrapnel at the end of an Ariana Grande concert
Abedi was once made a "subject of interest" himself, but his file was closed five months later in July 2014.
Home Office representative Cathryn McGahey QC gave the most extensive information about the security services' knowledge of Abedi prior to carrying out the attack during the public inquiry in Manchester.
The revelation came after a lawyer representing the UK traffic police told the investigation that the Abedi brothers who "did not act alone" and others who knew or suspected the bombing were still "at large" are.
Patrick Gibbs QC said on behalf of BTP that it was "obvious" that South Manchester suicide bomber Salman Abedi and his brother Hashem must have had help.
The security services received their first notice of him in 2010 and he was made a “subject of interest” in 2014, but the file was deleted four months later. Pictured: MI5 building in Vauxhall in central London
He cited the brothers' "complex and lengthy and carefully planned preparations" detailed in the investigation before and during the trial of Hashem Abedi.
The investigation, slated to run until next spring, looks at events before, during and after the attack – including the radicalization of Abedi and what the security services knew about him.
Ms. McGahey said some of the exact details could not be released and would only be heard by the chairman of the investigation, retired High Court Justice Sir John Saunders, his legal team and government lawyers during the closed hearings of the investigation.
But quality control said, "It's not a question of secrecy to hide failures."
Abedi was first known to MI5 on December 30, 2010 for its links to an address relevant to a Topic of Interest (SOI).
Three years later, an investigation by an SOI & # 39; A & # 39; suspected of being involved in planning a trip to Syria discovered a telephone contact with Abedi.
In March 2014, Abedi opened as an SOI but closed in July and the investigation into him ended "due to his lack of commitment to people of interest" for MI5.
A year later, MI5 found that Abedi had a phone in touch with another SOI & # 39; B & # 39; previously linked to and investigated with al-Qaeda to help others travel to Syria.
Police flocked to the Manchester Arena after the shocking attack three years ago
He also met B in person and MI5 assessed Abedi's extremism, although it was likely influenced by the contact. It was "unlikely" that B knew of Abedi's plans.
In the same year that information was received, Abedi was in contact with a long-time SOI C linked to extremists in Libya.
Again, MI5 C may have had a radicalizing influence on Abedi, who was then 18 years old, but had no evidence of involvement or knowledge of the Arena Plan.
MI5 also had intelligence services. Abedi traveled regularly to Libya and as of 2015 the service had "conflicting information" which it advocated for Isis.
On three subsequent occasions, Abedi was identified as a second level contact by three other SOIs in April 2016 and April and January 2017.
The SOIs involved were suspected of supporting or recruiting Isil in Syria or Libya.
And in both February 2015 and January 2017 he visited Abdalraouf Abdallah, a convicted terrorist, in two separate British prisons.
The 22 victims of the terrorist attack during the Ariana Grande concert at the Manchester Arena in May 2017
MI5 received information about Abedi twice in the months leading up to the attack, but at the time it was classified as possibly non-shameful or non-terrorist.
In retrospect, this message was highly relevant to the planned attack, but the investigation did not fully appreciate the importance of this information at this point.
Abedi's name also hit a "priority indicator" during a separate "data-washing exercise" as it was one of a small number of past topics of interest that deserved further consideration.
A meeting to review the results was scheduled for May 31, 2017, nine days after the bombing.
But even if MI5 had made other decisions in the months leading up to the attack, it might not have stopped the bombing, Ms. McGahey said.
It would have taken some time to build information and allocate resources to a large number of other ongoing investigations, she said.
The hearing was adjourned until Thursday morning.
Arena plotters are "still at large," the British traffic police attorney told the public
The brothers who carried out the attack at the Manchester Arena "did not act alone" and others who knew or suspected the bombing are still "at large" according to a public inquiry.
Patrick Gibbs QC, the British Transport Police (BTP) official in the public investigation into the atrocities, said it was "obvious" that South Manchester suicide bomber Salman Abedi and his brother Hashem must have had help.
Commenting on the Manchester investigation, Mr Gibbs said, "But what about the other potential killers, we don't know their names yet."
He cited the "complicated and lengthy and carefully planned preparations" of the brothers detailed in the investigation before and during the trial of Hashem Abedi.
Patrick Gibbs QC, British Transport Police (BTP) agent in the public investigation into the atrocities, said it was "obvious" that the Abedi brothers must have had help
He added: “We will all understand that these brothers did not act alone.
“They must have received technical and financial assistance, training and support from other people.
"Other people must have known, or at least guessed, what they were up to, and these other people are at large."
Mr. Gibbs suggested to the chairman of the inquiry, Sir John Saunders, that the "mountain" of money spent on the public inquiry would be worth it if other people were brought to justice.
He added, “If one or more of these mass murder accessories can be knocked to the ground at your trial and brought to justice, there is no question that it is money well spent.
"In other words, your request is likely our last chance to track down those without whose help and inspiration these murders could not have taken place."
(tagsToTranslate) Dailymail (t) Messages (t) Ariana Grande