The attacker, convicted terrorist Usman Khan who secured an early release from prison, was apparently attending the event and had returned for the afternoon session when he began his stabbing rampage.
Khan was convicted as part of a group of al-Qaida-linked terrorists that planned attacks on major sites in London, including Parliament and the U.S. Embassy.
"I want to thank the emergency services and members of the public for their huge bravery in responding to this suspected terrorist attack at London Bridge".
Khan had been conditionally released from jail last December after serving less than half of a 16-year prison sentence for terrorism, and was wearing a fake explosive device.
A spokesman for West Midlands Police said: 'There is no information to suggest that the arrested man was involved in the incident at London Bridge on Friday.
"As we saw the worst of humankind, we saw the very best of human spirit and London", Met Police Commissioner Cressida Dick said Saturday as she visited London Bridge.
"We know Jack would not want this awful, isolated incident to be used as a pretext by the government for introducing even more draconian sentences on prisoners, or for detaining people in prison for longer than necessary", they added.
The judge added that Khan shouldn't be released until he and the others were considered to no longer be a threat to the public.
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Convicted in 2012 for terrorism offences, Khan was known to United Kingdom authorities, Basu said.
Those convicted of a serious terrorism offence should face a mandatory minimum sentence of 14 years, he said later.
Merritt was reportedly a Cambridge University graduate who was working for its "Learning Together" initiative run by the Department of Criminology to promote prison-based education.
"I think there has to be an examination of how our prison services work and crucially what happens to them on release from prison".
"Jack was an intelligent, thoughtful and empathetic person who was looking forward to building a future... and making a career helping people in the criminal justice system", they said.
"We respectfully request that the media leave us to grieve in private at this very hard time".
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.
Authorities say he was not referred to the British Parole Board.
Mr Corbyn said police were "stuck with a situation where there was a credible threat of a bomb belt around his body and it's an terrible situation for any police officer, any public servant to be put in" as he backed the decision to kill the attacker.
The UK Prime Minister Boris Johnson commented on the incident, "It is important we get out of that habit and enforce the appropriate sentences for unsafe criminals, especially for terrorists".