Khan killed two people and wounded three while on conditional release from prison in the November 29 knife attack.
He was shot dead by police while wearing what proved to be a fake explosives vest on the iconic bridge in the heart of the UK capital.
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Khan had been serving a 16-year prison sentence for an Al-Qaeda-inspired plot to attack central London and was freed after being deemed to no longer be a risk to the public.
He was prevented from causing more harm by Londoners who jumped on him before the police arrived, tackling him to the ground and hitting him with whatever was at hand.
John Crilly, 48, who served eight years in prison for murder in a botched burglary, was attending a class for reformed convicts at the time of the attack, which came in the heat of Britain's general election campaign.
He told the BBC that he acted on "instinct" and "was screaming at (Khan) to blow it (the belt)... calling his bluff."
"I was prepared to probably lose my life," he said.
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Khan had taken part in the same convict rehabilitation programme as Crilly during some of his time in jail.
Crilly said he first tried bring down Khan with a wooden lecturn he grabbed from Fishmongers' Hall, where the class was being held, before using the fire extinguisher.
"The spray distracted him," he told the BBC.
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