British police have identified 22-year-old Youssef Zaghba, an Italian of Moroccan descent, as the third attacker in Saturday's violent rampage in London that killed at least seven people.

The announcement came a day after London's Metropolitan Police Service named two other men as attackers: 27-year-old Khuram Sharzad Butt, a British citizen born in Pakistan, and 30-year-old Rachid Redouane, who "claimed to be Moroccan and Libyan."

Zaghba "was not a police or MI5 subject of interest," according to the Metropolitan Police. Like Butt and Redouane, he lived in east London.

Police shot and killed the three attackers within eight minutes of receiving an emergency call, police said. They stressed that while they believe they know the attackers' identities, "formal identification is yet to take place."

The security forces have been raiding addresses in London. In a statement Tuesday, authorities said they arrested a 27-year-old man Tuesday morning. Twelve people who were detained in connection to the attack have been released without charge, police say.

Questions are being raised about whether British police missed crucial warning signs that could have prevented the attack.

Butt was known to police and was "openly fundamentalist," NPR's Eleanor Beardsley reports from London. "Neighbors say he tried to radicalize their kids in a public park."

In fact, Butt was one of the main characters in a television documentary called The Jihadis Next Door.

"Today, newspapers are asking how he was able to even walk the streets," Eleanor says. "The attack, the third in Britain in three months, has raised questions over the government's ability to protect Britain following cuts to police numbers in recent years."

ISIS has claimed responsibility for the attack, in a statement published by its Amaq news agency.

This is how the rampage unfolded, as The Two-Way has reported:

"The attack began at about 10 p.m., local time, when a van crossing London Bridge veered into pedestrians, crashing outside the Barrowboy & Banker Pub. Witnesses told the BBC that van hit 'five or six people,' then the attackers exited the vehicle and pursued others in a 'rampage' in which hundreds ran for their lives. One witness said he saw a woman stabbed '10 or 15 times' by the men, who he said shouted, 'This is for Allah.'

"The men then ran down a set of stairs and began stabbing people at a number of different pubs and restaurants in Borough Market, a historic fruit and vegetable market. Witnesses said people threw chairs and pint glasses at the men, who wore what police said were fake explosive vests."

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