The boss of MI5 has said he is “profoundly sorry” that the security service did not prevent the Manchester Arena terror attack.
An inquiry found the bombing might have been prevented if MI5 had acted on key intelligence received in the months before the attack.
In the wake of the findings, director general Ken McCallum also expressed deep regret that such intelligence was not obtained.
Two pieces of information about suicide bomber Salman Abedi were assessed at the time by the security service to not relate to terrorism.
But inquiry chairman Sir John Saunders said having heard from MI5 witnesses at the hearings into the May 2017 atrocity – that killed 22 people and injured hundreds – he considered that did not present an “accurate picture”.
I am profoundly sorry that MI5 did not prevent the attack
One officer admitted they considered a possible pressing national security concern on one of the pieces of intelligence but did not discuss it with colleagues straightaway and did not write up a report on the same day.
In his 207-page report, Sir John said: “The delay in providing the report led to the missing of an opportunity to take a potentially important investigative action.
“Based on everything the Security Service knew or should have known, I am satisfied that such an investigative action would have been a proportionate and justified step to take. This should have happened.
“Although I accept that Salman Abedi demonstrated some security consciousness and that this might have affected the efficacy of the investigative action that I have identified, there was the real possibility that it would have produced actionable intelligence.”
It could have led to Abedi, 22, being followed to the parked Nissan Micra where he stored the explosive and later moved it to a city centre rented flat to assemble, Sir John said.
The chair added that if MI5 had acted on the intelligence received then Abedi also could have been stopped at Manchester Airport on his return from Libya four days before the attack.
Sir John said: “It is also possible that a stop may have had a deterrent effect or led to investigative steps. There is a possibility that he had the switch for the bomb on him at that time.
“The chances of a port stop disrupting the attack may have been low, but I consider they cannot be discounted altogether.
The findings prompted heavy criticism nof the security services from families of the the 22 people murdered in the bombing.
In a statement, the boss of MI5 said: “The terrorist attack at the Manchester Arena was a terrible tragedy. The bomber killed 22 innocent people and harmed many others. My thoughts are with the families and friends of those killed, and with all those whose lives were changed by this appalling act of terrorism.
“Having examined all the evidence, the chair of the inquiry has found that ‘there was a realistic possibility that actionable intelligence could have been obtained which might have led to actions preventing the attack.’
“I deeply regret that such intelligence was not obtained. Gathering covert intelligence is difficult – but had we managed to seize the slim chance we had, those impacted might not have experienced such appalling loss and trauma. I am profoundly sorry that MI5 did not prevent the attack.”
MI5 “continually” works to improve efforts to tackle terrorism and since the attack had made “more than 100 improvements”, he added.
“But we are determined to do more. As the chair now considers his recommendations, we will engage fully. Where there are opportunities to strengthen the UK’s defences further, MI5 will act.
“We will continue to do everything in our power to keep our country safe from hidden threats.
“MI5 exists to stop atrocities. To all those whose lives were forever changed on that awful night: I am so sorry that MI5 did not prevent the attack at the Manchester Arena,” Mr McCallum said.
In March 2014, Abedi became a Subject of Interest (SOI) for MI5 over phone contact with another SOI but his case was closed four months later when he was deemed “low risk”.
He was also identified on six occasions as a direct or indirect contact of suspected extremists from December 2013 to April 2017.
During the inquiry, a number of MI5 witnesses - including a senior officer known as Witness J - and detectives from North West Counter Terrorism Police gave evidence behind closed doors.
The secret sessions - which included evidence about the two pieces of intelligence received months before the attack - were held so as not to compromise national security and the inner workings of MI5 and counter-terror police.
Sir John’s report on the circumstances surrounding the bombing at the end of an Ariana Grande concert also focused on the radicalisation of Manchester-born Abedi, of Libyan descent.
Abedi’s brother, Hashem Abedi, 25, was jailed for life after he was convicted of assisting the plot.
Sir John concluded: “The Abedi family holds significant responsibility for the radicalisation of Salman Abedi and Hashem Abedi.
“That includes their father Ramadan Abedi, mother Samia Tabbal and elder brother Ismail Abedi, each of whom has held extremist views.”
He said their views “influenced the development” of the brothers’ world views and it was “likely” Salman and Hashem also “fed off each other's ideas and radicalised each other”.
Convicted terrorist Abdalraouf Abdallah, a childhood friend of Abedi, also had an “important role” in his radicalisation while another Manchester associate Raphael Hostey - an Islamic State member killed in a drone strike in Syria - was also “likely to have been an influence”.
Andrew Roussos, whose daughter Saffie-Rose, aged eight, was the youngest victim of the attack, said the MI5 was guilty of a “cataclysmic failure”.
“It is clear from all of the evidence we have heard about Abedi that there were many opportunities for the security services to have ensured the bombing never happened.
“In my view, the fact that MI5 failed to stop him despite all of the red flags available demonstrates they are not fit to keep us safe and therefore not fit for purpose.”
Richard Scorer, principal lawyer at Slater and Gordon, who represented 11 of the families at the inquiry, said: “Today’s report has been deeply painful to read, but also eye-opening.
“But it is now very clear that there was a failure to properly assess key intelligence about Salman Abedi; a failure to put it into proper context, and - most catastrophic of all - a delay in acting on it.
“As a result of these failures, at the very least, a real possibility of preventing this attack was lost. This is a devastating conclusion for us.
“The failures exposed in this report are unacceptable.”
Home Secretary Suella Braverman said she was “committed to working with MI5, policing and partners to study the recommendations”.
“Together we will do everything possible to prevent a repeat of this horrifying attack,” she said.
Evidence into the circumstances leading up to and surrounding the atrocity was heard in the city between September 7 2020 and February 15 2022.
Thursday's third and final report into the terror attack followed two earlier reports.
The first was issued in June 2021 and highlighted a string of “missed opportunities” to identify Abedi as a threat before he walked across the City Room foyer and detonated his shrapnel-laden device.
Sir John’s second report last November delivered scathing criticism into the emergency services response to the bombing.
He ruled that care worker John Atkinson, 28, would probably have survived but for the failures on the night, while there was a “remote possibility” the youngest victim, eight-year-old Saffie-Rose Roussos, could have lived with different treatment and care.
