British police have also identified the third attacker as Youssef Zaghba, but said the 22-year-old was not subject of M15 (Britain's security agency) interest.
Police searching for a French man who has been missing since the London Bridge attack say they have recovered a body from the River Thames. The force said formal identification has not yet taken place, but Xavier Thomas's next of kin had been informed.
A total of 48 people were injured and London hospitals are continuing to treat 29 people - 10 of whom are said to be in a critical condition.
Much of the area around London Bridge remained cordoned off Tuesday and a minute of silence was observed in Britain as police continued to investigate Saturday's attack that killed seven people. The perpetrators drove a rental van into pedestrians on the bridge, then began attacking people with knives.
Rachid Redouane (center) and Youssef Zaghba have been named as the suspects in Saturday's attack at London Bridge.
Mr Rowley said that while Butt, who reportedly went by the name Abu Zaitun and was known to neighbours by the nickname "Abs/z", was known to the security services, there was no evidence of "attack planning" by him.
Butt is a Pakistan-born United Kingdom citizen known to the police and MI5 living in East London; he was so well known, that he was featured in a Channel 4 documentary about United Kingdom jihadis, The Guardian reports.
L'astronaute français Thomas Pesquet de retour sur Terre
Si l'aller a duré deux jours et demi, le retour ne durera que 3h20, soit l'équivalent d'un Paris-Marseille en TGV. Vient après l'activation de la propulsion principale qui va aider le vaisseau à se diriger vers la Terre .
Redouane was 30 and "claimed to be Moroccan and Libyan", police said.
"A 30-year-old man was arrested on suspicion of the commission, preparation or instigation of terrorist acts contrary to section 5 Terrorism Act 2006 and has been taken into custody at a south London police station under the Terrorism Act 2000".
Searches were underway at the residential property and a business address in Ilford, the latest in a series of raids since the weekend assault.
His mother told police a year ago that he had asked her for money to travel to Rome before he left on his abortive trip to Syria.
Butt and Redouane both lived in Barking in suburban east London.
Police have arrested 17 so far in connection to the incident in London, but have released 12 of them without charge.
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