Convicted terrorist Khan, 28, was armed with two knives and wore a fake suicide vest as he fatally wounded Cambridge University graduates Jack Merritt, 25, and Saskia Jones, 23, and injured others at the prisoner education conference they were all attending near London Bridge on November 29 2019.
Khan, 28, who had travelled to London from his home in Wolverhampton Rad, Stafford, had set upon Mr Merritt in the men’s toilets after strapping two large knives into his hands.
Marc Conway, a policy officer with the Prison Reform Trust, recalled coming face to face with a frenzied Khan.
Giving evidence at Guildhall in the City of London, he said: “I could see people fighting with Usman Khan.
“I thought people were messing about, then when I looked more closely I saw Usman Khan with his back to me and people moving out of his way, hitting him.
“I turned to the side and I saw the knives in his hand.”
He added: “Before I realised it was serious I said to people ‘They’re messing about in there, we’ve been invited to this nice building and you’re playing up’.
“Then I realised, and I said he’s got a knife, two big knives.
“It became apparent something serious was happening.”
Mr Conway said bystanders sought to hit Khan with various items, including a wooden chair, in a bid to stop him.
But he said: “He (Khan) wasn’t reacting in a way I think someone hit with a chair would react.
“There was some added motivation or strength there that I hadn’t seen before.”
Mr Conway said he phoned 999 and saw Khan burst out of Fishmongers’ Hall, making his way on to London Bridge, before turning to face those in pursuit, appearing to cross the knives he was holding across his face as he did so.
Mr Conway, who knew Mr Merritt, then ran across the bridge to try to help wrestle the knives from Khan, before realising that he had what appeared to be an explosive belt strapped to him.
Khan was tackled by members of the public with a decorative pike, narwhal tusk and fire extinguisher, and was then shot dead by police on London Bridge.
He said: “I just wanted to help. When someone said he’s got a bomb, and you realise that he’s got a belt round him, you felt like you was fighting for your life.
“I stamped on his hands, I may have put a few kicks in.
“One of the knives we managed to get rid of quite quickly, but the other was quite difficult to get off him.
“After a couple of shouts of ‘bomb, bomb’, I heard what I thought was a Taser.
“After a couple of seconds they (police) shot him (Usman Khan) twice.”
The inquests then heard from waitress Sandra Bufano, who had helped serve brunch at the event and was covering the cloakroom for a colleague when the attack began.
She heard screaming coming from the nearby men’s toilet, where Khan stabbed Jack Merritt, before he emerged and locked eyes with her.
“He was not doing anything, but just staring at me,” Ms Bufano said, describing the look as “very intense”.
Khan then stepped towards Ms Jones, who was about to leave belongings in the cloakroom, and stabbed her in the neck.
“He wasn’t rushing, he was completely calm and collected. He moved without rushing,” Ms Bufano said.
She saw Khan’s arm move upwards, and then told the jury: “At that point she screamed, at that point I thought something really bad is happening here.”
Ms Bufano then saw Mr Merritt looking unsteady on his feet with blood dripping down his arm, and “panicked” and ran.
Conference attendee Gareth Evans told the inquest how he tried to comfort Ms Jones as she lay fatally wounded.
Mr Evans said: “I took hold of her, she sort of collapsed, I sat down on the steps and I was talking to her.”
Appearing to wipe his eye, Mr Evans added: “I was trying to make sure she felt comfortable and safe.
“I said she was loved and she was beautiful and then everything else happened.”
Khan, 28, who was originally from Stoke and was living at flats on Wolverhampton Road, Stafford, before the attack, injured three more people during a five-minute rampage at a Learning Together event before being shot dead by police on London Bridge.
He was released from prison on licence in December 2018, halfway through a 16-year prison sentence, after he was convicted of terror offences in February 2012.
The jury inquests, taking place before coroner Mark Lucraft QC, continue.