Britain’s MI5 is to hold an inquiry into how it dealt with public warnings that the Manchester suicide bomber Salman Abedi posed a potential threat, the BBC reported on Monday.

MI5 was alerted to Abedi’s terrorist views at least three times, the BBC said.

It is highly unusual for British authorities to make public that the security service is conducting an internal investigation into possible lapses.

Interior Minister Amber Rudd told Sky News that this was a “right first step” for MI5 to take in the wake of the bombing that killed 22 people at a pop concert by U.S. singer Ariana Grande.

The security service will examine assumptions that were made about Abedi before the attack, and has launched a “post-incident investigation” into how the bomber was overlooked, the BBC said.

A separate report is also being prepared for ministers and those who oversee the work of the service, it added.

A source had told Reuters last week that Abedi was one of “a larger pool of former subjects of interest” whose risk remained subject to review by MI5.

Meanwhile, British police said they had arrested a new suspect on Monday over the Manchester bombings, bringing to 14 the number of people they have in custody over the attack.

Authorities detained a 23-year-old in the southern coastal town of Shoreham-by-Sea, more than 400 kilometers (250 miles) from Manchester.

In addition, police raided a property in a southern Manchester suburb as they step up their The attack, Britain’s worst in more than a decade, was carried out by British-born terrorist Salman Abedi, who detonated a powerful bomb at the exit of an Ariane Grande concert.

Several of the victims were children, the youngest being just eight. Scores were injured in the attack.

Abedi’s brother and father are being held in Libya.

On Sunday, police released photographs from security cameras showing Abedi on the night of the massacre, wearing jeans and trainers, a black bodywarmer and a baseball cap, with the straps of his backpack visible on his shoulders.

Britain has downgraded its security level from its highest level, but it still remains at “severe”, meaning an attack is highly likely.

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