The jury at Leeds Crown Court was directed by the judge to return a formal verdict of guilty of manslaughter on the grounds of diminished responsibility after four forensic psychiatrists agreed that he was severely mentally ill on the day of the attack.
The judge, Mrs Justice Smith, ordered that Stephen James Wilkinson, 31, should be sent to Ashworth Hospital, Merseyside, and that he should be kept there for a period without limit.
Wilkinson, of Middlesbrough, Cleveland, denied murdering Nikki but admitted manslaughter on the grounds of diminished responsibility. He also pleaded guilty to the attempted murders of Michelle Reeve, 13, and Emma Winter, 12.
The judge also sentenced him to be detained without limit in the hospital for each of these offences.
Nikki, 12, died of multiple stab wounds and Michelle and Emma were also knifed after Wilkinson, who was wielding a revolver, burst into the maths lesson at Hall Garth comprehensive, Middlesbrough, on 28 March last year and forced the teacher Graham Nellist to leave. Wilkinson was overpowered when the school's deputy head, Chris Bielby, and another teacher, Dave Eland, stormed in. Only later was the handgun found to be a harmless replica.
Wilkinson was also armed with three knives and an axe and the court heard how more children would almost certainly have died if the teachers had not intervened.
The judge acknowledged this and said she would be recommending that Mr Bielby and Mr Eland should be officially commended for their action.
Earlier the judge explained to the jurors why she had decided to direct them after a morning of submissions from the prosecution and defence counsels in their absence. After 45 minutes deliberation in her chambers she had decided to accept the submission from James Spencer QC, defending, that there was no issue to be left to the jury to decide.
There had been a burden on the defence during the trial, which began on Monday, to satisfy the jury that Wilkinson was suffering from a mental abnormality, she explained. She said: "You heard four very highly qualified forensic psychiatrists and they all said ... that he was suffering from a severe abnormality." Two of them had described it as paranoid schizophrenia and the other two said that it was paranoid psychosis, a similar condition.
"They all agree this was a severe mental illness which started in his late teens and had affected his life ever since. I have come to the conclusion that there really is no evidence on which I could give you a direction so that you could make a rational choice between two alternatives."
Sentencing Wilkinson, the judge said: "It is clearly beyond doubt that you have been suffering from a severe mental illness ... and I am satisfied your mental illness is such it is appropriate you should receive treatment in hospital."
Before passing sentence the judge made a point of explaining her decision to Nikki's parents, Peter and Diane, who were in the public gallery.
The judge said to them: "You may find this hard to accept and you do have my sympathy in that regard. There is not a person in this court who does not sympathise with your point of view, but I do hope you will accept this decision has not been taken lightly but with great care by the doctors, by counsel and by me."Reuse content