Will Cornick has also claimed he wanted to be stopped from carrying out the attack on Mrs Maguire at Corpus Christi Catholic College in Leeds in April 2014.
The comments provide one of the first public insights into his mindset at the time of the murder and are revealed in a report on a Leeds Safeguarding Children Board (LSCB) learning lessons review, launched after the Spanish teacher’s stabbing.
Cornick, now 18, pleaded guilty in November 2014 to murder and so was never questioned in court about his actions.
His meeting with the report’s independent author, Nick Page, is described as his first “meaningful interview” since his conviction.
The LSCB report concludes that “no one could have predicted or pre-empted Will Cornick’s attack on Ann Maguire”.
In it, Mr Page writes: “When I met with Will, I took him through a detailed discussion of the events leading up to and immediately after he stabbed Ann.
“He described going up the stairs to Spanish from break in a ‘red mist’, not conscious of his surroundings.”
Mr Page goes on: “Will now states that he wanted to be stopped from stabbing Ann.
“However, this needs to be considered in the context of the overall review report and the fact that he clearly and intentionally stabbed Ann to death.
“Will did not suggest that he wanted to be stopped in his interviews with the investigating officers, the Youth Offending Service worker, or the expert witnesses who interviewed him as part of the court proceedings.”
Today’s report confirms previously-released details of social media posts in which Cornick ranted about his hatred for Mrs Maguire, saying she “deserves more than death more than pain, torture and more than anything that we can understand”. On the morning of the murder, he had spoken to fellow pupils about wanting to kill the 61-year-old mother-of-two.
But, says the report, “the young people whom Will had spoken to viewed his statements as fantasy”.
It also floats the idea of national research into how to encourage children to share concerns with trusted adults.
Asked what could be done now to stop a similar attack, LSCB chair Mark Peel said: “We could take steps to completely eradicate the risk with respect to teachers but those would be so draconian as to undermine the actual task that teachers do which is quite personal and individual. If teachers were for example behind glass, clearly the degree to which they could teach would be undermined.”
Mr Peel said he hoped the review showed agencies responded to the tragedy with compassion and professionalism.
He said the report had received a very positive response from Mrs Maguire’s two sisters. But Mrs Maguire’s widower, Don, yesterday said it appeared to be “significantly different” from an early draft the family had seen some months ago. Among those paying tribute to Mrs Maguire were Pope Francis and then prime minister David Cameron.