A 16-year-old boy has been sentenced to life with a minimum term of 20 years for murdering popular teacher Ann Maguire, but was warned by a judge that he may never be released.

Mr Justice Coulson said the teenager, who has now been named as Will Cornick, showed a “total and chilling lack of remorse” after he stabbed Mrs Maguire, 61, seven times as she taught a class at Corpus Christi Catholic College in Leeds in April, when he was 15.

In an attack that shocked the nation, he chased Maguire, “stabbing her as she sought to escape”, Leeds Crown Court heard.

The judge set the 20-year tariff – the minimum time the teenager must serve in custody before he is released – but added that, having read about him, “it’s quite possible that day may never come”. He said Cornick’s pride in what he did and lack of remorse was “truly grotesque”.

The teenager remained seated while Mr Justice Coulson read his sentencing remarks.

He then stood and looked at the judge, with his head tilted to one side, as the sentence was passed. His expression did not change.

He did not appear to look at his parents, who were both visibly upset, as he was led from the dock.

Cornick, who the court heard came from a loving and supportive family, also spoke of attacking other school staff, including a pregnant woman “so as to kill her unborn child’’. He had winked at a fellow pupil before launching his assault.

I wanted to get caught. That’s why I did it in school. I wanted to be in jail

Outlining the case, prosecutor Paul Greaney QC said: “It is important that we should record that it is clear from the evidence that the parents of [the boy] are decent people and responsible parents.

“They are at a loss to understand how and why their son has turned out as he has and have co-operated fully with the police and with the prosecution.”

He said Cornick was in Maguire’s Spanish class and his academic reports “had generally been positive’’. There was nothing to indicate to the boy’s parents or teachers a risk of “homicidal violence’’.

But, he said, pupils noticed disturbing aspects to his personality.

The boy had told other children that he hated Maguire and wanted her dead.

The prosecutor said: “Late on the night of Christmas Eve 2013 and into the early hours of Christmas Day, the defendant exchanged messages with a friend on Facebook.

“In those messages he spoke of ‘brutally killing’ Maguire and spending the rest of his life in jail so as not to have to worry about life or money.’’

Cornick told a psychiatrist how he planned the murder.

The prosecutor said he took a bottle of whisky to school to celebrate after the attack.

Greaney told the court that the defendant said to the expert: “I decided on Sunday it was going to be a knife. I thought I was just going to go to school and wait for her lesson and do it.

“I wanted to get caught. That’s why I did it in school. I wanted to be in jail.’’

Greaney said the boy told other pupils he was going to attack Maguire on the morning of the murder. The boy showed some of them the knives he had with him.

Greaney said Cornick left a room next to where Maguire was teaching and winked at a fellow student before going to attack her.

There was no expression on the boy’s face as he stabbed her, one pupil said.

Greaney said: “Mrs Maguire was at her desk helping pupils. She was leaning over, looking at the work of a girl. The defendant approached his teacher and began to stab her in the neck and back.

“He attacked her from behind.

“Ann Maguire was 61 years of age, 5ft 2in in height and of slim build. The defendant was a full foot taller and was armed with a large kitchen knife.

“To describe his attack as cowardly hardly does it justice.’’

The prosecutor said Maguire fled but she was chased by the boy “stabbing her as she sought to escape’’.

Greaney said Cornick had earlier told pupils he wanted to attack other teachers, including a pregnant woman “so as to kill her unborn child’’.

The court was told Maguire’s friend and colleague, Susan Francis, heard screaming and rushed into the corridor where she found children “screaming in panic’’.

The prosecutor said Maguire ran towards her, holding her neck and saying: “He’s stabbed me in the neck.’’

The defendant, he said, then came after her, “in effect chasing her’’.

Francis pushed her friend into a workroom and held her foot against the door to keep the boy out.

Greaney said: “She was able to see [Cornick] through a glass panel in the door. His face was emotionless and he then walked away.’’