Correspondent Amy Welch has covered the public inquiry into the Manchester Arena attack from the start
There was a "significant missed opportunity to take action" which could have prevented the Manchester Arena terror attack, a report has found.
Failures to obtain "actionable intelligence" on bomber Salman Abedi meant he was able to build a "devastatingly destructive" device for six months after watching a video posted online by Islamic State.
Communication breakdowns between MI5 and Counter Terrorism Police North West officers meant intelligence was not shared, Sir John Saunders concluded in his third and final report following the Manchester Arena Inquiry.
"The reasons for this significant missed opportunity included a failure by a Security Service officer to act swiftly enough," he added.
The chairman said the most important was the failure to act on two pieces of intelligence received in the months before the attack but did not detail what they were.
Had the information been shared, Abedi’s return to the UK from Libya four days before the attack would have been treated "extremely seriously by the Security Service", he said.
Sir John added it "could have led to Abedi being followed to the Nissan Micra which contained the explosive", which, he said, might have prevented the attack.
A total of 22 people died after Abedi detonated a device at the end of an Ariana Grande concert on 22 May 2017.
The report, which looked at the radicalisation of Salman Abedi and the preventability of the attack, highlighted failings by the Security Service in their handling of the investigation.
It said MI5 and counter terrorism officers "underestimated" the risk posed by those travelling back from Libya.
If officers had stopped and searched Abedi as he arrived in Manchester Airport on 18 May 2017, Sir John found, there is "a real possibility" they would have found a switch used to detonate his homemade device.
While security services were aware of a threat from Libya, "the threshold that the Security Service applied when deciding whether to investigate any returnee from Libya was, in my view, too high and amounted to a risky position", he added.
The report found that a delay in providing information on a piece of intelligence by one security officer "led to the missing of an opportunity" to look further into Abedi.
"If the investigative action I have identified had been taken", Sir John said, "there was the real possibility that it would have produced actionable intelligence", which could have prevented the attack.
"We cannot know what would have happened, but there is at least the material possibility that opportunities to intervene were missed."
The report detailed an online video produced by Islamic State in November 2016 which described and demonstrated "in detail" how to make the explosive used in Abedi’s improvised device.
The similarities between the bomb created by Salman and Hashem Abedi and the one demonstrated in the video were "remarkable", experts told the Inquiry.
In the video, the presenter, dressed in a balaclava and camouflage combat clothing, "provided clear instructions on a step-by-step basis," Sir John said.
Sir John also said "human error" from CTPNW meant communication between Abedi and convicted terrorist Abdalraouf Abdallah were not passed to security services.
While in prison Abdallah had access to a mobile phone which was used to call Abedi 11 times between 16 January 2017 and 15 February 2017.
But, despite seizing the phone, records and data were not accessed and downloaded for a number of weeks, and even months.
Had this been done sooner, Abedi again could have been spoken to, Sir John concluded.
Chairman Sir John has also written a closed volume three report after the inquiry held 10 days of closed hearing at an unknown location in London, involving five separate witnesses for the Security Service.
The closed report is available to MI5, Counter-Terrorism Policing and, as the minister responsible for both organisations, Home Secretary Suella Braverman.
Announcing the sessions during the inquiry, Sir John said disclosing material in public would damage national security.
Justifying the hearings in his report, he said it allowed him to "squeeze out every last drop of learning", adding the opportunity to "hear directly from the officers is a valuable one" which assisted him to get to the "truth of what happened".
Finishing the report, Sir John said he was unable to say with any certainty whether the attack could have been prevented and whether additional action would have made a difference.
"It might have done, it might not have done," he said.
Following the publication of the inquiry findings, Home Secretary Suella Braverman said: "Today is a difficult day. On 22 May 2017, an act of pure evil took the lives of 22 people at Manchester Arena. My thoughts are with their loved ones and all those who had their lives changed forever.
"Over the past three years, the Manchester Arena Inquiry has carefully analysed critical evidence to ensure vital lessons are learned. I am grateful to Sir John Saunders and his team for their thorough and considered approach.
"I am 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."
Security Minister, Tom Tugendhat, added: "The Government, our security services and emergency services are wholly committed to learning the lessons of this unspeakable tragedy.
"We will do everything in our power to continue strengthening our country’s defences, and to keep the British people safe.
"I’m immensely grateful to all those who contributed their expertise, knowledge and experiences to the Inquiry, and to Sir John Saunders and his team for their thorough and meticulous work throughout the Inquiry."
Andy Burnham, Mayor of Greater Manchester, said: “At all stages Greater Manchester has faced up fully to the findings and we will do so again. Major changes have already been made to our emergency services and if more are needed as a result of this report we will do so.
“What has become clear through the stages of this inquiry is that, both at national and regional level, the country was not prepared for a terrorist attack of this nature in a city like ours.
"It is now beholden on all public bodies to use the findings of the inquiry to ensure all places are better prepared to protect people and respond to acts of terrorism.
“We know that today is another very difficult day for those bereaved, injured and affected by the attack at Manchester Arena.
Greater Manchester has stood with them from the beginning and our support will remain constant.”
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