The Fishmongers’ Hall killer was a "deeply, deeply disturbing, nasty, violent, self-regarding piece of work", the lawyer for one of his victims has told his brother.
The family of Jack Merritt questioned whether Usman Khan’s family had "looked away" instead of confronting him about his radical beliefs.
Khan’s brother, who has been given anonymity for the inquest, said the family "totally condemn his actions".
"First of all could I make sincere condolences to the family of Jack Merritt and Saskia Jones," he said.
"We are truly, truly sad for the events that have happened. Whoever’s been affected physically or mentally, we are really, really sad as a family. I just wanted to get that off my chest. We are really sorry."
Khan stabbed Jack Merritt, 25, and Saskia Jones, 23, both workers on the Cambridge University prisoner rehabilitation project, during a conference at the Fishmongers livery company on 29 November 2019.
Khan, who was wearing a fake suicide vest, was shot dead by armed police on London Bridge, 13 minutes after the attack began.
In his rented flat after his release, pathology tests suggested that Khan was using cocaine, but his brother, a self-confessed "party guy" said he "didn’t look high" when he saw him on Sundays.
Khan was also using sex lines and receiving sex texts, but his brother said they did not talk about that.
On 20 November at 5.18pm, Khan went into the Tesco Extra in Newport Road, Stafford, at 5.18pm to buy a roll of T-Rex gaffer tape, which he used to construct the fake suicide belt.
The inquest was told it happened within an hour or so of his brother leaving, and Nick Armstrong for the Merritt family asked: "Did you see anything in his demeanour that suggested all might not be well?"
"Nothing," his brother said. "If I had seen anything, I would have alerted, if I had seen any little thing.
"I went there, made a cup of tea and we were laughing and joking about the fare – he went to the wrong hospital, so I said I might as well wait to take him back."
Mr Armstrong said by then Khan had a "to-do list" of things he needed for his attack and asked: "Would you say you are a sensitive, curious man?"
He added: "I am suggesting early in his life there was something deeply, deeply wrong with your brother."
The inquest was shown extracts from a research interview conducted by Ruth Armstrong and a colleague Simon Larmour from Learning Together in March 2019, in which he spoke warmly about his victim.
"I had a good conversation with Jack, a half hour conversation," he said at one point, and at another: "I was speaking to Jack about this, don’t forget your experiences."
He talked about another prisoner conducting a "dirty protest" in jail and added: "I feel grateful, I say to Jack, you know the day was sunny I was walking, and I said for me what happens is after time something works out."
Mr Armstrong said: "He is talking warmly, as a friend then he attacks him. That was your brother – a deeply, deeply disturbing, nasty, violent, self-regarding piece of work.
"That was all present since childhood but you looked away, you saw none of that."
Khan’s brother, dressed in a blue collared shirt and with a thick beard and crewcut, looked down and mumbled a response.
Mr Armstrong accused Khan’s brother of "never wanting to challenge" his brother and of sitting in the prison visiting room trying to make sure he did not "stress him out".
But Khan’s brother insisted: "When we visited him, we see the progress, all we can see is his face, we don’t know what’s inside.
"We asked the prison officer, how’s he doing and he said, he’s a good lad, he keeps his cell tidy."
Mr Armstrong insisted: "These fundamental principles existed throughout out his life."
The inquest has heard that Khan had been involved in violence, bullying and forced conversions inside the jail but his behaviour had improved towards the end of his sentence.
Mr Armstrong questioned whether Khan had even changed, telling his brother: "He is not a very nice man, even pre the offence.
"He seeks some sort of derived status, he has always been this man, there has never been this fundamental change."
The inquest was shown images from the local paper, the Stoke Sentinel, which had Khan in the street with a black jihadi flag.
Mr Armstrong asked Khan’s brother: "At a time you say he was chilling with his friends and keeping himself to himself, he was literally standing in the street with a flag?"
His brother said: "That doesn’t look like a local street, that looks like a mile and a half, a couple of miles away."
But Mr Armstrong said: "This is not a man who is keeping his beliefs to himself he is trying to get attention for the causes that he espouses by standing in the street with a jihadi flag."
He was pictured with the radical preacher Anjem Choudary because he "wants to associate with people who are bigger and badder than he is", Mr Armstrong said.
In jail, he said Khan had made up a "bad boy" image, claiming he had been expelled from school, at the age of 14.
He had also "sought out" the hook handed preacher Abu Hamza by deliberately getting sent to the segregation unit at Belmarsh, Mr Armstrong said.
After Hamza’s extradition to the US, records showed he had asked for a 60p stamp after writing to Hamza in the Metropolitan Correctional Centre in New York to "express his sorrow at the move".
Even after Khan’s release, he showed off by boasting of his association with Charles Bronson, the notorious armed robber, while in jail.
When he was put on a Healthy Identity Initiative between November 2014 and August 2015, halfway through his eight-year prison sentence, the report said that he only want to "tell his side of the story" and "better himself".
He openly disagreed with risk assessment of him, could not provide any details that needed improving and said he "already had a positive self-image".
"I don’t recognise that person," Khan’s brother said.