Aamer Madhani

USA TODAY

One week after the Manchester Arena attack, British authorities confirmed Monday that the nation’s intelligence agency, MI5, has launched an internal investigation of how it handled information about suicide bomber Salman Abedi.

Interior minister Amber Rudd called the internal investigation the “right first step” for the intelligence agency that has come under scrutiny over how Abedi managed to carry out the May 22 attack at pop singer Ariana Grande’s concert that killed 22 and injured dozens more.

“There is a lot of information coming out at the moment about what happened, how this occurred, what people might or might not have known,” Rudd told Sky News. “And I think it is right that the MI5 takes a look to find out what the facts are.”

Abedi, 22, had been on intelligence officials’ radar prior to the attack, the deadliest terrorist incident in the United Kingdom since 2005. The Islamic State claimed responsibility.

MI5 was alerted at least three times to Abedi's extremist views, the BBC reports. His behavior also reportedly raised concerns from fellow congregants at Manchester’s Didsbury Mosque after he shouted at a prayer leader who condemned the ideology of the Islamic State militant in a sermon.

Authorities on Monday also released a new image of Abedi wheeling around a blue suitcase in Manchester that was gleaned from security video sometime in the days prior to the attack. Investigators have reviewed hundreds of hours of security camera video as they focus on the bomber's movements in the days leading up to the attack. Authorities urged the public to contact investigators if they saw Abedi with the suitcase or have spotted the suitcase alone.

"We believe Abedi was in possession of this case in the days before the attack at Manchester Arena," Detective Chief Superintendent Russ Jackson, of the North West Counter Terrorism Unit, said in a statement. "I want to stress that this is a different item than the one he used in the attack.

The image was captured on CCTV on May 22 in the city. "We have no reason to believe the case and its contents contain anything dangerous, but would ask people to be cautious," Jackson said.

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The bomber grew up in Manchester in a family of immigrants from Libya that fled their homeland in the early 1990s during the regime of Moammar Gadhafi. U.S. Africa Command reported after the attack that Abedi spent three weeks in Libya and returned to Manchester within days of the bombing.

Rudd took the unusual step of confirming the intelligence service’s internal probe as Britons prepare to head to the polls in 10 days to elect a new government, an election in which security and policing are now expected to be forefront of voters’ minds.

In a BBC interview, Rudd said MI5 is currently investigating 500 different plots and has identified 23,000 extremists, of which 3,000 are on a "top list." She said the intelligence agency is also in the process of hiring nearly 2,000 more recruits and its budget "has gone up significantly."

"We will make sure that we put the right resources in to keep people safe always," Rudd said.

On Monday morning, Greater Manchester Police announced it made its 16th arrest in connection to the bombing after in executed a search warrant in the Whalley Range area of Manchester — the same area where Abedi lived. Two of the 16 suspects have been released without charge, according to police.