The father of the teenager who murdered teacher Ann Maguire said his son "very much regrets what he did and is desperate to find a route to get better", an inquest has heard.
A statement by Ian Cornick was read out at the inquest into the death of Mrs Maguire, who was stabbed by his son, Will Cornick, at Corpus Christi Catholic School in Leeds.
Mr Cornick said he tries to visit his son in prison once a month.
Mr Cornick said that his son "struggles to express his emotions" and only really trusts his family.
He said he has repeatedly gone over the events of April 28 2014, when his son was 15, and said: "I cannot point to anything that could have forewarned anybody of what was to happen."
He added: "There was simply nothing I could point to in Will's demeanour prior to that Monday which helps me understand in any way what happened."
Mr Cornick, who is divorced from his son's mother, Michelle Leadbeatter, said he spent the weekend immediately before the tragedy on the Monday morning with his son and said it was "exceptionally ordinary" and "unremarkable".
Mr Cornick said his son did play violent video games, like his older brother but he said: "Both knew the difference between fantasy and reality".
He said he believes his son's personality changed after he was diagnosed with type one diabetes in 2010. He said Will became more introverted after that news.
Both Cornick's parents talked about a meeting they attended at school after he had got into trouble for missing a detention and had told them how much he disliked doing Spanish. They said his relationship with Mrs Maguire had broken down.
Mrs Leadbeatter said that the school gave her son an internal exclusion but they asked for him not to be left alone due to his type one diabetes.
They also asked that Mrs Maguire was not left to discuss anything with him alone as the relationship was bad.
She said in her statement that, at one point, her son told her: "I can't stand Mrs Maguire" and she recorded this in her diary.
Mrs Leadbeatter said she was concerned that her son was not getting access to the treatment he needs due to his Category A prisoner status.
On Monday, Detective Superintendent Nick Wallen, from West Yorkshire Police, told Wakefield Coroners' Court that Cornick had shown no remorse during his officers' dealings with him.
Cornick was jailed for life for Mrs Maguire's murder and ordered to serve a minimum of 20 years in custody.