The Manchester Arena bomber had been a “subject of interest” and opportunities to stop him were missed, a review says.
Its author, David Anderson QC, said it was conceivable Salman Abedi’s attack, which killed 22 people, could have been avoided had “cards fallen differently”.
But he said it was “unknowable” whether reopening investigations into Abedi would have thwarted his plans, adding: “MI5 assesses that it would not.”
Greater Manchester Police said its officers would “never stop learning”.
After the Manchester bombing and three terror attacks in London this year, counter-terror police and MI5 conducted internal reviews. Mr Anderson carried out an independent assessments of their findings.
The major internal reviews, which remain largely secret, are summarised in Mr Anderson’s report, and show:
- The Manchester bomber Salman Abedi had been a “Subject of Interest” for MI5 – meaning someone they were investigating – between January and July 2014, and then again in October 2015
- On two occasions in the months before Abedi attacked, MI5 received intelligence, but its significance was not fully appreciated at the time and, in hindsight, was “highly relevant” to the planned attack
- Abedi was identified by MI5 as one of “a few dozen” people who needed further consideration. The meeting to do that was due to take place on 31 May, nine days after the attack
- There was no security service port alert against Abedi, so he was not questioned at the border when he returned to the UK from Libya four days before the attack
The reviews also showed the two other attackers who had been on MI5’s radar were Khuram Butt, the leader of the London Bridge and Borough Market attack, and Khalid Masood who targeted Westminster Bridge.
Butt had been identified by MI5 and the police as someone who wanted to attack the UK two years earlier.
He was still a “live subject of interest” who was under investigation at the time of the attack, though more for his intention to travel to Syria and for radicalising others.
He was also the main target of “Operation Hawthorn” – but this was suspended twice because of a lack of resources after the Bataclan attack in Paris and the Westminster Bridge attack.
Operation Hawthorn had resumed and was running on the day Butt attacked.
Mr Anderson, a former independent reviewer of terror legislation, said: “Despite elevated threat levels, the fundamentals are sound and the great majority of attacks continue to be thwarted.
“But the shock of these incidents has prompted intensive reflection and a commitment to significant change.
“In particular, MI5 and the police have identified the need to use data more effectively, to share knowledge more widely, to improve their own collaboration and to assess and investigate terrorist threats on a uniform basis, whatever the ideology that inspires them.”
Terror attacks this year
- A man in a hired car drove into pedestrians on Westminster Bridge then stabbed a police officer outside Parliament on 22 March
- A suicide bomber targeted young people at the end of a concert by US singer Ariana Grande at Manchester Arena on 22 May
- A van hit pedestrians on London Bridge before three men got out and stabbed people in nearby Borough Market on 3 June
- A group of Muslim worshippers were hit when a van mounted the pavement and drove into them in Finsbury Park, in north London, on 19 June
The home secretary said nine terror attacks have been prevented in the UK since the Westminster attack in March.
In a statement to the Commons, Ms Rudd said MI5 and the police had made 126 recommendations.
These included issues such as data sharing and analysis and how so-called “closed subjects” should be managed, as well as a new approach to managing domestic extremism, particularly of right-wing groups.
“We will shortly be announcing the budgets for policing for 2017/18, and I am clear that we must ensure counter terrorism policing has the resources needed to deal with the threats that we face,” she told MPs.
The Met Police said the number of dangerous, radicalised individuals was “a major issue”.
Commissioner Cressida Dick said her force needed “to make rapid progress in implementing the recommendations, many of which require new technology, better infrastructures and resources”.
The Mayor of Greater Manchester Andy Burnham said the report would be difficult reading for the people of his city.
“It is clear that things could, and perhaps should, have been done differently and that wrong judgements have been made,” he said.
But, he said, it should reassure the public to know MI5 were closing in on Abedi.
It would be much more worrying if nothing had been known about the attack, he added.
Chris Phillips, a former head of the National Counter Terrorism Security Office, said: “When you look back, within terrorism, you will always find some way that we could have stopped something.
“I always equate it to spinning plates. They’ve got hundreds and thousands of plates spinning at any given time.
“Someone has to make some risk-assessed decisions as to who is at the top of the pile to be watched.”
The current threat level for terrorism in the UK is severe, meaning an attack is highly likely,