The man named by police as the London Bridge knife attacker was a convicted terrorist released on licence last year.
Usman Khan, 28, who was living in the Staffordshire area, was jailed in 2012 for his role in a failed attempt to bomb the London Stock Exchange and plotting to set up a terrorist training camp.
He was originally handed an indeterminate sentence, which meant that he would not have been released until he was no longer deemed to be a risk to the public.
In 2013, the Court of Appeal quashed the sentence, replacing it with a 16-year fixed-term. Having served the minimum eight years, he was automatically released on licence.
Questions are now being raised regarding why he was considered suited for release, and how effectively he was being monitored upon his return to the community. Indeterminate sentences were deemed unlawful in 2012 and scrapped.
In a statement released overnight, Met police assistant commissioner Neil Basu said: "This individual was known to authorities, having been convicted in 2012 for terrorism offences. 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.”
More details of how the attack unfolded have also emerged.
Police say the attacker attended an event on Friday afternoon at Fishmongers' Hall for an organization called Learning Together; the event was the five-year anniversary of a prison reform initiative organised by academics from the University of Cambridge.
The attack is said to have started inside the venue, on the north side of the bridge, before the suspect left the building and went onto the bridge, where he was first tackled by members of the public before police intervened. He was shot dead by specialist armed officers.
Two people, a man and a woman, were killed during the attack. Three others, a man and two women, were also injured and remain in hospital.
Throughout the night, counterterror officers searched an address in Staffordshire.
Basu said: “Whilst we’re still in the early stages of the investigation, at this time we are not actively seeking anyone else in relation to the attack.”
Met commissioner Cressida Dick, speaking on Saturday afternoon, confirmed this.
"We do believe this person was acting alone, as far as we can tell," she said. "And we will continue to investigate the circumstances that led to this moment."