But, with "no intelligence to suggest that this attack was being planned.the investigation had been prioritised accordingly".
This undated handout photo provided by the Metropolitan Police shows Khuram Shazad Butt and Rachid Redouane.
Three knife-wielding attackers on Saturday had unleashed a terror rampage here, ploughing a van into pedestrians on the iconic London Bridge before stabbing revellers in a nearby market, killing seven people.
The Canadian Christine Archibald, a French national and a Briton were among the dead, while other French people, a Spaniard, Australians and a New Zealander were among the 48 who were injured in what May called "an attack on the free world". Ismail Abedi, 24, the brother of the suicide bomber Salman Abedi, was released without charge after he was arrested during the police investigation.
The officials spoke on condition of anonymity because they were not allowed to discuss details of the case. He used two different birthdates that would make him either 25 or 30, authorities said.
It was the third terrorist attack in Britain in the past three months. "One witness said he saw a woman stabbed '10 or 15 times" by the men, who he said shouted, 'This is for Allah'.
Zaghba was reportedly working in a London restaurant and had not been seen in Italy since 2016.
London's mayor, Sadiq Khan, said in a statement late Saturday night that "Londoners should be aware that there will be additional armed and unarmed police officers on our streets from tonight in order to keep Londoners, and all those visiting our city safe". A new search was underway Tuesday in Ilford, just north of Barking, as authorities tried to determine whether the group had accomplices.
Residents at a block of flats in Barking - where a number of arrests were made on Sunday - said they recognised the attacker and that he had lived in the area for around three years.
Assistant Commissioner Mark Rowley urged anyone with information about the latest attack to come forward.
Robert Quick, Britain's former counter-terrorism chief, has told the Guardian government cuts to police funding have damaged attempts to prevent attacks. The Islamic State group has claimed responsibility.
After a brief pause, election campaigning resumed on Monday, with security dominating the agenda ahead of Thursday's vote.
Butt, a Pakistani-born British citizen, was known to intelligence agencies. Redouane had not aroused any suspicions. "We have given increased powers to the police to be able to deal with terrorists, powers which Jeremy Corbyn has boasted he has always opposed", she said.
Butt is a father of two and had previously worked in KFC and in the customer service for the London Underground as a trainee.
The British need a strong and inspiring leadership but the million dollar question is will Theresa May prove equal to the task.
The Conservative Party's lead over Labour has narrowed markedly from 20 points or more when May called the election in April to a range between one and 12 points now, although the Conservatives are still widely expected to win a majority.
Less than half a mile (one kilometre) away, people stopped to look at dozens of bunches of flowers left at the southern end of London Bridge, which was cordoned off by police vehicles.