Twelve others have been arrested in the investigation. Butt, Redouane and a third man were all shot dead by police within minutes of the attack.
Another terrorist, Rachid Redouane, was named Monday afternoon.
Assistant Commander Mark Rowley said: "Inquiries are ongoing to confirm the identity of their accomplice".
London Mayor Sadiq Khan said Monday that the actions of the attackers were perverse and poisonous, adding that they had no place in Islam.
The Islamic State terror group, also known as Daesh, has claimed responsibility for the London Bridge rampage, while the attack has sparked fears Britain is in the grip of a spate of copycat incidents.
British officials declined to say how numerous bridges are being retrofitted with barriers, but at least three bridges in the city center have already been modified, Sky News reported.
Another 36 men and women are now in hospital, 21 of whom are in a critical condition, according to NHS England. That fact provided a line of attack for Corbyn, who called on May to resign even as he said the best remedy was to vote her out. As the mayor of London, I want to send a clear message to the sick and evil extremists who commit these disgusting crimes: we will defeat you.
In the latest outrage, three terrorists killed seven victims and injured dozens more in the London Bridge area on Saturday night.
President Donald Trump for a second day lashed out at London's mayor on Twitter in the wake of a deadly terror attack in the city.More news: Senate intelligence panel requests Trump campaign documents -WashPost
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Mohammed Shafiq, chief executive of the Ramadhan Foundation, said Butt called him a "Murtad" - traitor in Arabic - when he confronted Choudary about his support of terrorism days after the murder of Lee Rigby in 2013. "Chrissy was a bright light to many, and her generosity, kind spirit and huge heart for her work in responding to issues of addictions and homelessness at the centre inspired us all", they wrote in a statement.
A French national was also killed in Saturday night's attack but has not yet been named.
She said providing more firearms for London police wouldn't be a sensible solution to the increased tempo of attacks, saying the strategy of having special mobile units of heavily armed officers is effective.
"We grieve the loss of our attractive, loving daughter and sister who was 30 years old".
"This was an attack on London and the United Kingdom, but it was also an attack on the free world", British Prime Minister Theresa May said Monday.
But May's own record came under fire from the Labour Party, which - according to opinion polls questioned for their reliability - has closed the gap on her Conservatives ahead of Thursday's general election. Masood was shot dead by police.
May served as home secretary for six years before becoming prime minister last year, a period in which the number of police dropped by about 20,000 officers.
The Mayor of London Sadiq Khan led the vigil, which was held less than a mile from London Bridge and Borough Market - where the attack was carried out.
On May 22, Salman Abedi, a British-born suicide bomber, killed 22 people and injured scores of others at an Ariana Grande concert in Manchester in northwestern England.