The IT consultant, who does not want his identity revealed, is a resident of the apartment block in Barking, east London, from where 12 people were arrested on Sunday in connection with the attack that left at least seven dead and 48 injured on Saturday night in the London Bridge area.
"The arrests were all made from two ground-floor apartments. I have played table tennis twice with one of the men. He is possibly one of the three attackers," he had said when The Telegraph initially called him. He was unwilling to name the man as the information was still classified. Nor did he have the heart to see the pictures of the terrorists' bodies in the media for fear of his apprehension being confirmed.
But once the Metropolitan Police revealed the identity of two of the assailants a few hours later, with photographs, there was no doubt left.
"He was a good player. I lost to him both times we played. He was very well-mannered.... This feels so creepy now," he messaged after this newspaper sent him the picture tweeted by the police while he was on his way back from work to the building that both he and Khuram called home.
The Bengali techie, who is in the UK for seven years now, knew Khuram to be born of a Pakistani father and a Somalian mother. "He stayed with his wife, a seven-year-old elder son and an infant. He was a shade shorter than me, had a long beard and wore a skullcap and trousers reaching down to his ankles all the time. Neighbours say he was religious-minded," he says.
"Everyone in the building had been saying it's him. I am stunned at the thought of how a normal family man could do this."
Khuram is suspected to have been one of the three assailants who had used a van to mow down pedestrians on London Bridge before attacking people in nearby Borough Market with knives.
Describing the address - Elizabeth Fry Apartments on King's Road - the Calcutta boy says: "It has a ground-floor lobby where the letter boxes hang. Residents are free to set up portable table tennis boards there and play. The ground-floor folks - the other flat I believe housed some Ethiopians - had one. They used to regularly play amongst themselves."
The University of London postgraduate was woken up on Sunday by the wailing of sirens around 8am.
"From my balcony, I saw the area below cordoned off and several police vans and ambulances lined up. Overhead, there was a helicopter hovering. I tried to go out but was stopped by an armed guard. There was one on every floor. The guard asked me to go back to my flat and stay indoors. It was an unnerving sight as policemen in London are rarely armed. I switched on the TV and logged in to the Net but there was nothing. I could not ask the few neighbours I am friendly with in the building as I did not have their phone numbers."
Finally, there was information on the BBC around 11am of a raid taking place in the area. "A while later, a local news website posted a helicopter shot of my building, identifying it to be the site of the raid. It was a nerve-wracking wait, as I feared an encounter. The only person I could speak to was a cousin in another part of London."
Of the four apartments on the ground floor, two had been evacuated before the raid ensued. "The police had used mild explosives to smash the door open. The suspects were scattered. Some were near the building entrance from where they were picked up. I saw a man being led away by three policemen.
Later, bystanders said one had tried to run and there were shots fired. I did not hear any of that as houses here are almost sound-proof with double layers of glass to keep off the cold."
Once the guard manning the floor left, it signalled the end of the raid. "We were allowed to leave the house after 4pm."
But even on Monday, the two ground-floor apartments remain sealed as does the main entrance.
"We are going in and out through the back door between forensic tents set up on either side, producing identity proofs and signing to be allowed passage."
His wife left on a work trip for the US last Friday. "Possibly she has no clue about the drama in our house."
He did call his parents in Barrackpore on Sunday.
"They have asked me to leave the building as soon as I find alternative accommodation."
-The Telegraph Calcutta