"We do have to look again at the sentencing system", he said.
United Kingdom counterterrorism police on Saturday searched for clues into how a man imprisoned for terrorism offences before his release previous year managed to stab several people before being tackled by bystanders and shot dead by officers on London Bridge.
The video shows one person pursuing the knife-wielding attacker with the sea creature's tusk while another sprayed the assailant with a fire extinguisher.
The judge had deemed Khan and two others "the more serious jihadists", and said they should not be released until they were no longer a threat to the public.
The violence erupted less than two weeks before Britain holds a national election December 12.
Amag, the jihadi organization's news agency, posted a bulletin claiming the attacker, known terrorist Usman Khan, was "responding to calls to target the nationals of Coalition countries".
Khan was sentenced to prison to a minimum of eight years and was also found guilty of planning to go to Pakistan to get "terrorist training".
He had been convicted in 2012 as part of an Al-Qaeda-inspired group plotting a Christmas bomb attack in 2010 on major sites including the London Stock Exchange, the US Embassy and the home of Prime Minister Boris Johnson, who was then London's Mayor. "They should serve every year of [their] sentence", Mr. Johnson added.
Police is searching the address of the suspect who attended an event Friday called, "Learning Together", at Fishmonger's Hall.
Metropolitan Police chief Cressida Dick said she was "deeply saddened and angered that our city has again been targeted by terrorism".
A hero who was inside Fishmongers' Hall when the London Bridge attacker began his knife rampage grabbed a narwhal tusk from the wall to try and fight him off, it has been reported. The group's plans included the camp in PoK, where under the guise of a madrassa they would offer arms training for attacks in Kashmir, and also a 26/11 style attack on the United Kingdom parliament.
Tour guide Stevie Hurst, who ran from his vehicle to the scene, told BBC radio that "everyone was just on top of him trying to bundle him to the ground".
"And it was while he was subject to these conditions that he performed this horrific attack yesterday", Fisher said.
One man in a suit and tie - identified by media as a police officer - was later seen carrying a large knife away.
Inmates are usually released half-way through the type of determinate sentence he was given, and time spent in custody before trial may have been taken into account. The Parole Board said on Saturday that it had not been involved in deciding Khan's release. He was released from prison on licence in December 2018, Met Police Assistant Commissioner Neil Basu said.
"A great deal of work is being done right now to make sure that the public is protected", he added. She thanked police and emergency services "as well as the courageous individuals who put their own lives at risk to selflessly help and protect others".