The British police on Monday arrested a trainee pilot in connection with the Manchester concert bombing last week.
The 23-year-old was held on suspicion of terror offences in Shorehan-by-Sea, West Sussex, Greater Manchester Police said.
Violet Mainda, who owns a hairdresser's salon beneath the flat where he was arrested, said she believed the man who lives there was training or had trained to be a pilot.
He became the 16th person to be arrested in connection with the bombing, which killed 22 people and injured more than 100. Two were released without charge, while 14 men remained in custody for questioning, the police said.
Also, the UK security service MI5 on Monday launched two urgent inquiries into how it missed the danger posed by bomber Salman Abedi, the Guardian newspaper reported. MI5 was alerted at least three times to the bomber's "extremist views", according to reports.
Home Secretary Amber Rudd refused to comment on whether opportunities were missed to spot the murderous intent of Abedi before the deadly attack, as national security became the major issue in the general election campaign.
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But in a highly unusual move for British authorities, she confirmed that MI5 was reviewing its practices.
"I do think it is right that MI5 take a look at their processes to ensure that they work to the best of the possible limits to make sure that we keep people safe," she told BBC.
Police also searched a detached property in Whalley Range, south Manchester.
The fallout from the attack triggered an intense war of words across the political spectrum, with Rudd claiming that there would be a greater risk of another atrocity if Labour leader Jeremy Corbyn became the Prime Minister.
Investigators believe Abedi, whose parents come from Libya, may have received terrorist training in the country, where some areas are believed to be a safe haven for jihadis, the daily reported.
He returned to Britain from Libya just days before exploding a homemade-bomb packed with metal bolts and screws at the Ariana Grande concert at Manchester Arena on May 22.
Teachers and religious figures in Manchester who knew Abedi raised concerns about his extremist views on multiple occasions and over several years.
MI5 is believed to have conducted a quick review of the intelligence held about Abedi last week, but the inquiry was limited as the agency's focus and resources were poured into the manhunt and recovering the materials linked to the bomb.
The second review will be more detailed and look at the decision-making around Abedi before his attack.
Abedi had been examined by security service case officers in the past, but by last Monday was one of a pool of 20,000 one-time Islamist jihadi suspects. He was not one of the 3,000 people under active investigation.