London's Metropolitan Police said one attacker was Khuram Shazad Butt, aged 27. Butt was previously known to police and domestic spy agency, MI5 and was a British citizen who had been born in Pakistan, the police said.
“However, there was no intelligence to suggest that this attack was being planned and the investigation had been prioritised accordingly,” police said.
Butt appeared in a Channel 4 documentary entitled “The Jihadis Next Door” about British extremists that was broadcast last year, British media reported.
The second attacker was named as Rachid Redouane, aged 30, who also went by the identity Rachid Elkhdar and was not known to police. Redouane claimed to be Moroccan and Libyan.
Police said they were still working to establish the identity of the third attacker.
“I would urge anyone with information about these men, their movements in the days and hours before the attack and the places they frequented to come forward,” national counter-terrorism police chief Mark Rowley said in the statement.
“At any one time MI5 and police are conducting around 500 active investigations, involving 3,000 subjects of interest.
“Additionally, there are around 20,000 individuals who are former subjects of interest, whose risk remains subject to review by MI5 and its partners,” he said.
Police said they now had 10 people in custody after releasing two of the 12 people arrested on Sunday.