Ismail Abedi was arrested the day after his brother (pictured) carried out the attack
Ismail Abedi was arrested in Chorlton, Manchester, on May 23 after his brother killed 22 people at an Ariana Grande concert at Manchester Arena a fortnight ago.
According to police, three of the 14 people arrested after the suicide attack were released without charge last week.
The investigation has so far found Abedi largely assembled the nail bomb on his own, according to anti-terror officers.
Russ Jackson, head of the Northwest Counterterrorism Unit, said CCTV footage and other evidence had shown “Abedi himself made most of the purchases of the core components” of the explosive.
He added: “Many of his movements and actions have been carried out alone during the four days from him landing in the country to committing this awful attack.”
Abedi largely built the explosive himself, according to police London Bridge terror: Scenes as armed police respond Sun, June 4, 2017
At least two people have died after being after reportedly being struck by a van on London Bridge on Saturday night.
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Armed police responding to the incident at London Bridge
More than 100 concertgoers were also injured by the bombing.
A benefit concert for the victims of the attack was held at Old Trafford cricket ground Sunday.
Grande performed as part of a line-up including Justin Bieber, Coldplay, and Katy Perry for the charity event.
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The news comes days after armed police killed three terrorists on London Bridge Saturday night London terror raids Sun, June 4, 2017
Police have raided a block of flats in Barking in connection with last night's London Bridge terror attack.
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As police continue their investigations following the June 3 terror attacks, a block of flats in Barking is raided for possible suspects
The concert went ahead despite the attack on London Bridge on Saturday, which left seven dead and dozens more injured.
The identities of two of the three attackers, who ploughed a van into pedestrians on the bridge before moving into nearby Borough Market to stab and kill revellers indiscriminately, have now been revealed by police.
Khuram Butt, 27, and 30-year-old Rachid Redouane, both from Barking, London, carried out the sickening assault before being shot dead by armed police.