A senior officer at British Transport Police has accepted the force let the public down on the night of the Manchester Arena attack.
Assistant Chief Constable Sean O’Callaghan has been giving evidence to the public inquiry into the atrocity.
He agreed mistakes were made, including having no officers in the foyer where bomber Salman Abedi hid before the blast which killed 22 people.
Mr O’Callaghan said the attack had “happened on [BTP’s] watch”.
Twenty-two people were killed and hundreds more were injured as they left an Ariana Grande concert on 22 May 2017.
The inquiry previously heard there were no police officers on patrol when 22-year-old Abedi made his journey from Victoria Station to the City Room.
“The attack that happened that night happened on our watch,” Mr O’Callaghan, who was not working for BTP at the time, said.
“There is not a day that goes by when BTP doesn’t consider that.”
He added: “Did we let the people down?
“It was our responsibility to police that arena and that attack happened when we were policing it, there were police officers planned to be deployed to the site of the attack and they were not there – so in that term, yes.”
But Mr O’Callaghan denied the threat of terrorism at the Manchester Arena had been disregarded by the force.
“There was no specific mitigation taken in relation to [the Ariana Grande concert] other than officers on patrol,” he said.
“The information officers had at the time was up to 100 concerts a year had been going on at the arena…there was nothing to focus the mind on people planning a policing response that a person-borne IED was plausible at that time.”
The inquiry at Manchester Magistrates’ Court heard risk assessments by BTP for events at the arena were never documented.
Mr O’Callaghan said: “The process we adopted in our own risk assessments, in my view, was not to a suitable standard.”
But he said there was no policy in place to say the assessments should have been documented.
Mr O’Callaghan said there had been a number of improvements to police planning for events at the arena.
This includes specific counter-terrorism briefings for all officers before deployment, formal documented risk assessments specific to each event and more multi-agency meetings.
The inquiry, which is examining the background to the attack and if any opportunities to prevent it were missed, continues.