Police said Butt had been investigated by police and Britain's domestic spy agency MI5 earlier, but he was not deemed enough of a threat to warrant tight monitoring.
"While formal identification has yet to take place, detectives believe they now know the attackers' identities", the police statement said "All three men were confronted and shot dead by armed officers within eight minutes of the first call".
Almost 50 others were injured.More news: Man bitten on Delta flight by another passenger's dog
NHS England said 36 people remained in hospital, with 18 in a critical condition. Redouane also is said to have used another identity, that of Rachid Elkhdar.
The Mayor will be joined by senior representatives of the Metropolitan Police, the British Transport Police, London Ambulance Service, London Fire Brigade and civic, faith and community leaders.
On Tuesday, counter-terror officers were searching a property in Ilford, east London, after entering the address at around 01:30 BST. Witnesses told the BBC that van hit "five or six people, ' then the attackers exited the vehicle and pursued others in a "rampage" in which hundreds ran for their lives". All three have been claimed by the Islamic State group. Commissioner Mark Rowley said.
But an announcement - made before the Manchester and London Bridge attacks - that they planned to make some of the elderly pay more for their care saw that lead start to shrink, to between one and 12 points now.
Simon Howell, chair of Team London Bridge, the business improvement district for the London Bridge area praised local businesses as well as the police and emergency services.More news: Antoine Griezmann confirms Atletico Madrid stay after transfer ban upheld
One of the victims in Saturday's attack was identified as Chrissy Archibald, a Canadian who had moved to Europe to be with her fiance. The second, James McMullan, 32, was from the London suburb of Hackney.
London Bridge rail and Tube stations both reopened early on Monday morning. They are in the process of installing barriers on Waterloo Bridge and Lambeth Bridge. The three attackers had been shot dead.
"The Conservative plans mean another 400 million pounds (S$714 million) of cuts to the Met, as well as between 184 million pounds and 700 million pounds a year due to their changes to the police funding formula", Khan, a member of the opposition Labour Party, said in an e-mail.
Ms Boden's family described her in a statement as an "outgoing, kind and generous person".More news: Paul Pierce Gets Eviscerated For Bold Kevin Durant Take After Game 2
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