British police have named the third London attacker as 22-year-old Youssef Zaghba, an Italian of Moroccan descent from east London.
The Metropolitan police said he was not a "person of interest" before Saturday's attack.
Earlier police admitted that one of the other attackers was on their radar as a member of an outlawed radical Islamist group, but said an investigation into him had been downgraded as there was no evidence he posed an imminent threat.
Khuram Shazad Butt was associated with the banned extremist group al-Muhajiroun, co-founded by notorious hate preacher Anjem Choudary, and appeared in a 2016 documentary called "The Jihadis Next Door."
Khurah Shazed Butt, left, and Rached Redouane have been named as the London attackers by the Metropolitan police.
Assistant Commissioner Mark Rowley of London's Metropolitan Police acknowledged that Butt, a British national born in Pakistan, was known to authorities. "However, there was no intelligence to suggest that this attack was being planned and the investigation had been prioritized accordingly," he said.
Butt was one of three men who rammed a van into pedestrians on London Bridge in the city's center before launching a stabbing spree in bars and restaurants at the nearby Borough Market. Seven people died and 48 were injured.
Questions have swirled over why police were unable to do anything about Butt. And just two days before the UK election, Prime Minister Theresa May has faced a barrage of criticism for cutting 20,000 officers from the police force in her time as Home Secretary.
What we know about the London Bridge attackers
A Met Police spokesperson told CNN that an investigation into Butt started in the summer of 2015, during which police received a call to the anti-terror hotline. The probe continued but was moved into "the lower echelons of investigations."
A woman and child lay flowers near London Bridge on Monday to remember the victims of the attack.
A woman and child lay flowers near London Bridge on Monday to remember the victims of the attack.
"Looking back over the information we had at the time, so far, there is nothing to show that poor decisions were made. We will probably discover communications during that period that we couldn't access that would have change the situation," the spokesperson said.
UK Foreign Secretary Boris Johnson said that the country's intelligence agencies had questions to answer.
"People are going to look at the front pages today and they're going to say, 'How on earth could we have let this guy or possibly more through the net?'"
Twelve people were arrested after the attack but have all now been released without charge, the Met Police said on its Twitter account Monday. It also reported that officers had raided an address in Ilford, east London, in the early hours of Tuesday morning.