A 15-year-old pupil stabbed teacher Ann Maguire to death in a "completely irrational act stemming from a deep-seated grudge", a senior detective has told the inquest into her death.
Detective superintendent Nick Wallen said the 61-year-old "stood absolutely no chance whatsoever" when she was attacked in her classroom by teenager Will Cornick as she taught Spanish at Corpus Christi Catholic College, Leeds, in April 2014.
Det Supt Wallen was giving evidence on the first day of the inquest into Mrs Maguire's death. The hearing is due to last two weeks at Wakefield Coroners' Court in West Yorkshire.
The officer took the jury through the "shocking" events at the school, describing how the "slight" and "petite" teacher was "ambushed" by a "strapping 15-year-old lad".
Answering questions, Det Supt Wallen agreed that, on the day Cornick killed Mrs Maguire, he told "at least 10 other pupils precisely what he was going to do – where he was going to do it and how he was going to do it".
But the detective said none of the children took him seriously and it was not reported to any staff.
He told the inquest: "He was a young man who was prone to say things that weren't true. That's the reason that, on the day, most people who Will spoke to thought, 'That's just Will, that's what he does'."
The officer added: "I would say she stood absolutely no chance whatsoever."
Killer 'showed knife to other children'
Det Supt Wallen said Cornick and his family were not known to the police or any safeguarding agencies before the incident.
The jury heard how Cornick pleaded guilty to murder and was sentenced to life in prison with a minimum tariff of 20 years.
Nick Armstrong, representing Mrs Maguire's husband, Don, and their four children at the inquest, asked the officer about how Cornick told other children what he was going to do on the day of the murder and even showed some at least part of the knife, which Det Supt Wallen called a "vicious-looking thing".
Det Supt Wallen said he specifically instructed his officers investigating the murder not to ask the children why they did not report what Cornick had said.
He told the jury: "It would be wholly wrong to sit here and raise that perhaps all this could have been avoided if a 15-year-old boy had told the teacher. I think that would be wholly wrong."
Mr Armstrong told the court: "There is no question of the family apportioning blame." Mr Armstrong said he was asking these questions in order that the right lessons are learned.
Det Supt Wallen said that "with hindsight" the police, the school and Cornick's parents would have stopped him.
He said: "We cannot, from what happened, have foreseen this enormous crescendo of rage and violence that took place on that day."
The detective said Cornick had never shown any remorse to police for what he did.
The inquest continues.