The Manchester Arena Inquiry Thursday published the third and final volume of its report into the suicide bombing at an Ariana Grande concert in Manchester in May 2017, revealing that MI5, Britain’s security services, missed an opportunity to take actions which may have prevented the attack. Retired High Court Judge Sir John Saunders chaired the public inquiry.

MI5 identified two pieces of intelligence about bomber Salman Abedi as potential national security concerns. However, there was a failure by the responsible officers to discuss the significance of the information with colleagues and to write and deliver a report on the same day.

The prompt delivery of such a report would have meant that Abedi’s return to the UK four days before the attack would have been treated extremely seriously by MI5 and could have led to him being port stopped under Schedule 7 of the Terrorism Act 2000 at Manchester Airport on his return. The report notes that this in itself may have had a deterrent effect. It could also have lead to the discovery of the switch for the bomb, which Abedi “more likely than not” had on his person as he passed through the airport.

Furthermore, investigative steps would almost certainly have been taken. Abedi would likely have been followed by MI5 officers to his Nissan Micra, in which they would have found his explosives.

The conclusion gave rise to a notable public apology from MI5 Director General Ken McCallum, who stated that “had [MI5] managed to seize the slim chance [it] had, those impacted might not have experienced such appalling loss and trauma.” He further noted that he is “profoundly sorry that MI5 did not prevent the attack.”