Assistant Chief Constable John Murphy says: "Everyone at Bedfordshire Police is utterly shocked and appalled by the sickening actions of this individual and we are pleased he is now facing a significant time in jail.

"This was a lone individual whose plans [for the school shooting] were fortunately disrupted.

"I would like to pay tribute to the bravery of his family, the neighbour who called police, our officers who apprehended him, and all who have worked tirelessly to secure the compelling evidence which ensured he was brought to justice."

Nicholas Prosper was still living with his mother, brother and sister as he plotted to murder them in the block of flats in the Marsh Farm area of north Luton.

His father, Ray, had separated from his wife Juliana Falcon when Nicholas was nine years old.

The court heard his relationship with his father was "strained", but Ray had maintained contact with his children.

Nicholas Prosper's father and other relatives hugged as they left court.

Footage from Bedfordshire Police bodycam shows the moment Nicholas Prosper is arrested near his home after killing his mother, brother and sister.

Concluding her comments, the judge paid tribute to Prosper's family, whose noise as they were being killed alerted neighbours in their tower block in the Marsh Farm area of Luton.

She says: "Their deaths are almost certain to have saved the lives of many children, and the community owes them a debt of gratitude."

Prosper's dad Ray is sobbing as he is led out of court.

Nicola Haseler
BBC News, Luton Crown Court

It’s hard to imagine what it must be like for Prosper’s dad, Ray, to listen to what his son did to his two younger children - especially in front of a packed court room.

At Prosper's first court appearance just days after the murders, his dad shouted out: "I still love you, son. It's not your fault, OK?"

Yesterday in his victim impact statement, Mr Prosper referred to having lost four members of his family.

Judge says: “You intended to unleash disaster on the community of Luton.

"You remain highly dangerous and it may be you will never be released."

Nicholas Prosper, 19, has been jailed for life, with a minimum prison term of 49 years before he will be considered for release on parole.

Nicholas Prosper is refusing to stand while the judge passes sentence.

He remains seated with his head in his hands.

The judge says although she has been "troubled by this shocking case” she will not issue a whole life order.

Her reasons are because his school killing had been thwarted, because he had entered guilty pleas and was only aged 18 at the time of the crimes.

The judge says Prosper's undiagnosed autism spectrum disorder (ASD) did not impair his ability to understand his own conduct.

"You are intellectually capable of logically understanding the impact of your actions," the judge says.

"Your cognition and ability to refrain from murder were not diminished."

The judge has outlined Prosper's psychotic traits and says he has shown "no remorse and no sorrow" for the killings.

The judge adds that he has expressed pride in his crimes.

When asked if he would try to commit another mass murder, the court hears that the killer told his psychiatrist: "Well that's their job [the authorities], to stop me getting the weapons if I'm released."

In her sentencing remarks, the judge is also considering Prosper's plan to continue the killing at his former primary school in Luton.

"A murder spree for the sole purpose of glorifying the perpetrator in the history of mass killers is what you intended," she says.

Considering her sentence the judge says: “I am conscious that nothing I can do or say can reflect the worth of Juliana's, Kyle's and Giselle's precious lives.

“You are indisputably a very dangerous young man.”

She is outlining the guidelines relating to life sentences and whole life orders.

The judge recalls police were met with a “scene of horror” at the Prosper home in their Luton tower block.

Evidence showed his sister had hid in the living room before Nicholas Prosper shot her in the head.

He had placed a book called How To Kill Your Family by his mother's legs.

Later, after his arrest, Prosper was "inappropriately cheerful”, the judge said.

"The boy you idolised, Adam Lanza, shot his mother in bed before driving to Sandy Hook," says the judge.

Nicholas Prosper continues to look at the ground as his father is supported by family members. He cannot stop crying as the details are read to the court.

Nicholas Prosper's father Ray Prosper is in tears as the judge explains how his son had shot his sister and stabbed his brother.

The judge described how police officers found bloody hand prints and evidence he had reloaded the shotgun twice.

Describing the morning of the killing the judge says: "Later it was established you were disturbed by your mother who had noticed something extremely wrong.

"When your mother realised you had a gun she struggled with you before you shot her in the head in the hallway."

The judge explains how Prosper carried out reconnaissance at his old primary school in Luton and had drawn diagrams of the classrooms at St Joseph's Catholic Primary School.

She says he had written a note next to the drawing which read "kill all".

The judge adds: "You filmed yourself acting out the killing in the kitchen."

The judge noted that she was told at 08:45 Prosper had refused to attend the hearing.

Now he is in court, she told him: “You have to face the consequences of your actions.”

Prosper still has his head in his hands as Mrs Justice Cheema-Grubb addresses him.

Mrs Justice Cheema-Grubb described Prosper's crimes as "chilling" as she recounted how he wanted to kill more people than had died at the the Sandy Hook school massacre in the US.