British police on Tuesday named the third London Bridge attacker as an Italian national of Moroccan descent, and Italian officials said they had passed on their concerns about him to British intelligence officials past year.
Italian authorities said Zaghba had been stopped and questioned in Italy but had not been charged with any crime.
At the time of the attack, Zaghba was working in a London restaurant, Italian media said.
Zaghba, 22, was not a subject of interest for the police or the MI5 intelligence agency, officials said.
The alarm bells should have been deafening, CBS News correspondent Charlie D'agata reports.
Butt's friends and neighbours spoke about their interactions with him, and reports said his family's hotel in Pakistan had been searched. Last month, he was spotted urging people in east London not to participate in the June 8 general election.
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He then visited Area 60 of the cemetery, where numerous fallen heroes of the war in Iraq and Afghanistan were laid to rest. Without a word, he slowly laid the wreath at the Tomb of the Unknowns.
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Ms Boden worked at Guy's Hospital in London Bridge. In a letter posted outside his gym, the Ummah Fitness Centre said staff would "help the police in any way we can".
Butt, 27, was previously known to authorities, but there wasn't enough intelligence to suggest he was planning an assault.
The other attacker was Rachid Redouane, 30, who went by the alias Rachid Elkhdar and is believed to be of Moroccan or Libyan origin. He was not on police radar.
In particular, the revelation that at least one of the attackers, Khuram Butt, was well known to security services has raised concerns that they lack the resources to prevent attacks. "He would always bring his kid out into the lobby", said Chigbo. He was a really good person.
Australian authorities are working with United Kingdom police to determine what happened to Brisbane woman Sara Zelenak, 21, who is still missing after being separated from friends on London Bridge during the attack.
The pair and one other man were shot dead by police after killing seven people and injuring 48.
Butt and Redouane both lived in Barking in suburban east London.