Video report by ITV News Correspondent Max Walsh
The London Bridge terrorist who killed two people acted alone, the Metropolitan Police chief has said.
Usman Khan, 28, was released on licence last year after serving half of his 16-year sentence but was able to embark on a deadly stabbing spree in central London on Friday, killing a man and a woman and injuring three others.
Asked if she could confirm that the attacker was acting alone, Met Commissioner Cressida Dick said: "At this stage that is our understanding. Of course, the investigation will continue following all the most pressing and obvious lines of inquiry and we must make 100% of that of course.
"That will be done as quickly as possible, I'm not prepared to give you a moment-by-moment commentary on the investigation."
In the aftermath of the incident, questions will now be asked as to how and why Khan was released by authorities.
The attacker was attending a prisoner rehabilitation event organised by the University of Cambridge, where he "threatened to blow up" Fishmongers' Hall, where the conference was taking place, at around 2pm.
The parole board said Khan "appears to have been released automatically on licence (as required by law), without ever being referred to the Board".
Prisoners are usually released halfway through a determinate sentence but Khan had served less than seven years when he was freed on licence in December last year.
Speaking at the scene of the attack, Prime Minister Boris Johnson said: "It is clear to me that this guy was out, he'd served half of his sentence.
"He was out on automatic early release and I have long said that this system simply isn't working.
"It does not make sense for us as a society to be putting people convicted of terrorist offences, of serious violent offences, out on early release."
Security minister Brandon Lewis refused to say whether the attack was a failure by authorities.
Mr Lewis repeatedly refused to comment on the specifics of the incident, but said the government needed to look into whether sentences for the most serious crimes are tough enough.
He said: "We take what action we need to do and we believe is right under the advice of the police and look at all of the lessons learned from any case as quickly as we can to ensure people's safety."
Chris Phillips, a former head of the UK National Counter Terrorism Security Office, said the current criminal justice system was "playing Russian roulette" with the lives of the public.
He said: "The criminal justice system needs to look at itself.
"We're letting people out of prison, we're convicting people for very, very serious offences and then they are releasing them back into society when they are still radicalised.
"So how on earth can we ever ask our police services and our security services to keep us safe?
"I've said it a few times today, we're playing Russian roulette with people's lives, letting convicted, known, radicalised Jihadi criminals walk about our streets."
Khan was convicted of terror offences in 2012 and ordered to serve at least eight years behind bars for his role in an al-Qaeda style plot to bomb the London Stock Exchange and build a terrorist training camp on land in Pakistan-controlled Kashmir owned by his family.
Met Police assistant commissioner Neil Basu said: "He was released from prison in December 2018 on licence and clearly, a key line of enquiry now is to establish how he came to carry out this attack."
The Metropolitan Police confirmed the attacker had been shot dead by police after members of the public restrained him.
The Times reported Khan was released from prison last year after agreeing to wear an electronic tag so his movements could be monitored.
The Stoke-on-Trent-based radical, along with two co-conspirators, originally received an indeterminate sentence for public protection but this was quashed at the Court of Appeal in April 2013.
A police search believed to be linked to the London Bridge investigation is being carried out at a three-storey block of flats in Wolverhampton Road, Stafford, close to the town centre.
A police photographer and search teams entered one of two doors at the front entrance to the block on Saturday morning, while two uniformed officers were present at a cordon outside the building.
Retired police officer Justin Lightfoot, who lives in a nearby street, said he instantly recognised Khan when a friend showed him a mugshot of the 28-year-old in a media report on Saturday morning.
Mr Lightfoot said: "The only thing I've seen is him just walking past my house.
"I've seen his picture this morning online and when I saw that obviously I recognised him."
He added: "It's just frightening when somebody lives so close to you - you don't know what's going on so near to your home."
Mr Lightfoot added: "I've seen him for probably the last three or four weeks. Whether he was there longer or not I don't know."
Another resident, whose house overlooks the flats, said: "I've certainly seen police there before, but what for I'm not sure."I haven't seen the man who lived there for at least a week or so."
What do we know about how the attack unfolded?
Khan was wearing a fake suicide vest when he was killed on London Bridge on Friday afternoon in full view of horrified onlookers.
Footage shows members of the public trying to stop Khan, with one person seen dousing him with a fire extinguisher while another tried to corner him using a five-foot narwhal tusk.
Speaking before chairing a meeting of the Government's emergency committee Cobra on Friday night, Prime Minister Boris Johnson said he had "long argued" that it is a "mistake to allow serious and violent criminals to come out of prison early and it is very important that we get out of that habit and that we enforce the appropriate sentences for dangerous criminals, especially for terrorists, that I think the public will want to see".
Khan was attending a conference on prisoner rehabilitation organised by University of Cambridge-associated Learning Together at Fishmongers' Hall and "threatened to blow up" the building.
Professor Stephen Toope, Vice-Chancellor of the University of Cambridge, said he was "devastated" that an event organised by its Institute of Criminology was targeted in the attack.
He said: "I am devastated to learn that yesterday's hateful attack on London Bridge may have been targeted at staff, students and alumni attending an event organised by the University of Cambridge's Institute of Criminology.
"We are in touch with the Metropolitan Police, and awaiting further details of the victims.
"We mourn the dead and we hope for a speedy recovery for the injured. Our thoughts are with all their families and friends."
Mr Basu said police believe that the attack began inside the Fishmongers' Hall "before he left the building and proceeded onto London Bridge, where he was detained and subsequently confronted and shot by armed officers.
Heroic members of public tackled attacker before police arrived
"Extensive cordons are likely to remain in place for some time and I would ask the public to continue to avoid the area.
"Public safety is our top priority and we are enhancing police patrols in the City and across London."
Thomas Gray, 24, was among a group of men who dragged Khan to the ground near Fishmongers' Hall.
The tour firm manager said he stamped on the terrorist's wrist to try to make him release one of two large knives he was carrying.
Tom Gray, a tour guide who was working in London, helped apprehend the suspect. He told ITV News how he "stamped on the wrist" of the attacker, attempting to free the knife from his grip.
He claimed the attacker had two knives, one taped to his wrist. He was one of several members of the public who rushed to respond to the attack.
Election campaigning suspended as PM praises 'brave' first responders
The Conservatives, Labour and Liberal Democrats have cancelled all their campaigning for the General Election on Saturday.
Prime Minister Boris Johnson paid tribute to "the extraordinary bravery of those members of the public who physically intervened to protect the lives of others and for me they represent the very best of our country and I thank them on behalf of all of our country".
He added: "Anybody involved in this crime and these attacks will be hunted down and will be brought to justice."
He later described the deaths of two members of the public at London Bridge as "heartbreaking" and said there would be an "enhanced" police presence on the streets following the attack.
Mr Johnson said he had "long argued" that it is a "mistake to allow serious and violent criminals to come out of prison early and it is very important that we get out of that habit and that we enforce the appropriate sentences for dangerous criminals, especially for terrorists, that I think the public will want to see".
Speaking in Downing Street ahead of the Cobra meeting, Mr Johnson declined to say whether the individual was known to the security services or the police before the incident took place.
Labour leader Jeremy Corbyn tweeted: "Shocking reports from London Bridge. My thoughts are with those caught up in the incident. Thank you to the police and emergency services who are responding."
Jo Swinson, leader of the Liberal Democrats, praised "brave police who are dealing with it with professionalism". She said her thoughts are with those affected.
London Mayor Sadiq Khan thanked members of the public who risked "their own safety this afternoon".