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The Manchester bombing: unknown unknowns and ‘hindsight bias’

The May 2017 Manchester Arena bombing could have been prevented, a report by the former Independent Reviewer of Terrorism Legislation has revealed. The 22-year-old attacker Salman Abedi, who killed 22 people and injured 512 others, had been a “subject of interest” to Britain’s Security Service (MI5) in 2014 and 2015 but was classed as a “low residual risk” to national security and his case was closed.

David Anderson QC’s report suggests there were opportunities to reopen the case, raising the possibility the attack could have been stopped. MI5 twice received intelligence reports which – had their significance been “properly understood” – would have reopened the investigation into Abedi. The intelligence was not “fully appreciated” and judged to “relate not to terrorism” but possible “nefarious activity or criminality”. Abedi was just one of a number of closed subjects of interest (SOI) whose case needed “further consideration”. A meeting to review the evidence was scheduled for May 31, 2017 – nine days after the Manchester Arena bombing.

MI5 had also missed the opportunity to place a port alert on Abedi following a visit to Libya in April 2017. Had they done so, Abedi could have been questioned and searched by counter-terror police four days before the attack. As with the Westminster Bridge attacker, 52-year-old Khalid Masood, Abedi was judged to pose little threat, yet struck with devastating results.

The findings form part of a review requested by Home Secretary Amber Rudd to provide “independent assurance” of internal reviews by the police and MI5, to assess intelligence and decisions before the attacks, and to “identify whether the processes and systems … can be improved”.

Greater Manchester Mayor Andy Burnham said Anderson’s report would be a “difficult read” for Mancunians, adding:

It is clear that things could, and perhaps should, have been done differently and that wrong judgements have been made.

The report led to a series of headlines suggesting MI5 had been caught napping. BBC News claimed the attack “could have been stopped”, The Financial Times ran with the story that Abedi could have been “prevented”, while The Daily Mail suggested MI5 had missed a series of red lines and were “alerted months” before the Manchester Arena blast. One commentator concluded that Anderson’s conclusions are “damning for MI5”. The implication being a so-called “intelligence failure” had occurred.

Yet headlines like these are misleading, neglecting the nuance in Anderson’s report that the decision to ignore or misinterpret the intelligence on Abedi was “understandable” in the circumstances, overlooking the complex nature of counter-terror investigations. So could the Manchester bombing really have been prevented?

Unknown unknowns

For the security services, piecing together the intelligence jigsaw is a difficult process. Post-mortem reviews often suffer from hindsight bias. Complex issues become easy to interpret. Intelligence previously considered irrelevant, becomes suddenly important. Knowing the end result often provides clarity where there was none at the time.

“Hindsight can sometimes see the past clearly – with 20/20 vision”, concludes the 9/11 Commission report. In her classic study of the attack on Pearl Harbor, intelligence academic Roberta Wohlstetter found it “easier after the event to sort the relevant from the irrelevant signals”. Intelligence before an event is “obscure and pregnant with conflicting” messages.

Intelligence agencies are far from the all-seeing and all-knowing entities of popular imagination. The very nature of intelligence means that the information available to the security services is often incomplete. Remember this classic bit of intelligence speak from US Defence Secretary Donald Rumsfeld in February 2002?

We know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns – the ones we don’t know we don’t know.

Lord Butler’s review of intelligence on Iraqi Weapons of Mass Destruction (WMD) also makes it clear that “intelligence seldom acquires the full story”. When collected, the information is “sporadic and patchy”. In these circumstances, intelligence gaps are to be expected.

Talk of failure also overlooks the growing tempo of counter-terror operations in the UK. On Tuesday, MI5’s Director General Andrew Parker told ministers that his service had prevented “nine terrorist attacks” in the previous 12 months. Since the 2013 killing of Fusilier Lee Rigby, 22 attacks had been foiled. MI5 and counter-terrorism police continue to be inundated with potential threats.

Amber Rudd revealed to parliament there were over 500 live operations – up by a third since the start of the year – with a further 3,000 extremists categorised as “subjects of interest”. A further 20,000 individuals have been investigated and may pose a threat in future. The security services have to prioritise threats – sometimes with tragic results.

Intelligence failure?

In 2004, MI5 surveillance of the ringleaders of a fertiliser bomb plot, known as Operation Crevice, picked up two of the future July 7 suicide bombers – Mohammed Sidique Khan and Shehzad Tanweer. At the time, both were marginal figures. Continued surveillance of the Crevice cell led to successful prosecutions of others but Khan and Tanweer remained off MI5’s radar until the 7/7 attacks. The pair killed 52 commuters on the London transport network with their co-conspirators. Questions were again asked as to how two terrorists fell through the gaps of an inquiry and went on to kill. But hindsight made it easier to connect the dots that MI5 had missed.

Anderson’s report highlights that problems continue with the security services’ strategies for dealing with “low level” subjects of interest that may suddenly pose a threat, a concern raised by the Parliamentary Intelligence and Security Committee in 2013. But claims that the Manchester Arena bombing could have been stopped are too simplistic.

The report acknowledges the “inherent uncertainty” of whether more could have been done, while, on the balance of probability, a “successful pre-emption … would have been unlikely”. Abedi could have been stopped, for Anderson, had “the cards fallen differently”. In reality, they rarely do. Simplistic headlines that the attack could have been prevented fail to understand the complicated situation facing the security services and do little to bolster public confidence in the UK’s counter-terror effort.

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