Two of the London Bridge terrorists have been named by police as it emerged one of the attackers was known to security services.
Khuram Shazad Butt, a 27-year-old British citizen born in Pakistan, and Rachid Redouane, who claimed to be Moroccan-Libyan, carried out the deadly assault in which seven people died and dozens more were injured on Saturday night.
Officers at Scotland Yard said they are working to identify the third accomplice, while 12 people who were arrested in east London in the wake of the murderous rampage have been released without charge.
Britain's top counter-terrorism officer Mark Rowley said Butt was known to the security services, but there was no evidence of "attack planning" by him.
The father-of-two, who reportedly appeared on Channel 4 documentary The Jihadis Next Door, was investigated in 2015 but was part of a probe "prioritised in the lower echelons of our investigative work", Mr Rowley said.
The disclosure means that perpetrators in all three of the terrorist outrages to hit Britain this year had at some point appeared on the radar of authorities.
Butt, who reportedly went by the name Abu Zaitun, was known to neighbours by the nickname "Abs/z" and was allegedly an associate of radical hate preacher Anjem Choudary.
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.
He was on the radar of the police and MI5, and was reported to anti-terror hotline by a concerned member of the public
Security sources in Ireland confirmed Redouane, 30, married a British woman in Dublin in 2012 and lived in the Rathmines area of the city.
He also used the name Rachid Elkhdar, and claimed to be six years younger.
It is not clear when he came to the Republic or how long he stayed but it is believed he used Irish jurisdiction to get a European Union permit which allowed him to be in the UK.
An Irish security source described the murderer as having "extensive immigration history related to the UK".
Both killers lived in Barking, east London, and it is not yet known how the two men knew each other - with work to understand more about the trio and their connections still under way.
During the eight-minute long slaughter, the three knifemen ploughed into pedestrians on London Bridge using a van and went on to stab people in Borough Market with 12-inch knives.
The attackers, wearing fake suicide vests, were shot dead by eight officers after police unleashed a hail of 50 bullets upon them.
Thirty-six people remain in London hospitals, with 18 in a critical care.
As the nation collectively grieves following the third terror attack to hit the country in three months, a minute's silence will observed on Tuesday at 11am in memory of the victims.
Londoner James McMullan, 32, and 30-year-old Canadian Christine Archibald were the first victims killed in the attack to be named.
An unnamed French national also died in the rampage, with two others missing, the French foreign affairs minister Jean-Yves Le Drian said.
Scotland Yard said one person is still believed to be missing, and that family liaison officers have been deployed to support the victims' loved ones.
On Monday evening, a crowd of all ages and races stood quietly for an impeccably observed minute's silence at a vigil a short walk away from the scene of Saturday's bloodshed.
A book of condolence, already signed by Prime Minister Theresa May, will also open on Tuesday at Southwark Council's headquarters in Tooley Street.
Mrs May states in her message that British values are "superior to anything offered by the preachers and supporters of hate".
The Islamic State terror group, also known as Daesh, has claimed the London Bridge rampage, while the attack has sparked fears Britain is in the grip of a spate of copycat incidents.
Detectives would like to hear from anyone with information about the men, particularly places they may have frequented and their movements in the days and hours before the attack.