The U.K. has now been hit with three major terror attacks in the space of just three months, leading to an increased focus on how the police try to stop these attacks. But media reports in Italy said Italian authorities had alerted their British counterparts about his movements.
Police investigating the terror attack at London Bridge, in which eight people died, have made another arrest.
The police have come under scrutiny following the identification of the attackers because one of them was known to the authorities.
The three men wore fake suicide vests as they drove a white van into pedestrians on London Bridge, before stabbing revellers in the nearby Borough Market area. "What happened, how could he possibly be on a Channel 4 programme and be committing atrocities like this?' That is a question that will need to be answered by MI5, by the police, as the investigation goes on".
Zaghba, who is said to have been born in Morocco to a Moroccan father and an Italian mother, was stopped at Bologna's Marconi airport on March 15, 2016, while he tried to take a flight to Turkey.
Prosecutors said Zaghba had left Morocco in 2015 and headed for London, but visited his mother occasionally in Italy.
Police said they were still working to establish the identity of the third attacker.
Neighbors described Butt as an avid weightlifter and Transport for London confirmed he worked for London Underground in customer service before leaving last October.
Assistant Commissioner Mark Rowley said an investigation into Butt had been downgraded as there was no evidence he posed an imminent threat.
Police said they now had 10 people in custody after releasing two of the 12 people arrested on Sunday.
Khan warned Tuesday that proposed budget cuts to the Metropolitan police would make London more unsafe.
The crowd observed a one-minute silence at Potters Fields Park, a short distance from the scene of the attack that killed seven people and injured dozens of others. A Moroccan-Italian dual national, it has emerged he had tried to join the Islamic State group in Syria past year and was notified to Britain as a suspect figure after being intercepted by Italian authorities. Borough Market, a popular gathering place, remains closed as more evidence is gathered.
"I feel like I did what any other person would have done", he said.
Campaigning for the general election on Tuesday, Theresa May faced repeated questions about how the home office, which she ran for six years, police and intelligence services dealt with the information relating to the attackers. Within minutes, the attackers are shot dead and another police vehicle arrives as people are seen running for their lives.