At the sentencing hearing at Luton Crown Court on Wednesday, Justice Bobbie Cheema-Grubb said she had considered handing Nicholas Prosper a full life order in prison but opted against that given his age — he was 18 at the time of the shootings — and the fact that he had pleaded guilty,

Last month, Prosper admitted at a hearing to murdering his mother Juliana Falcon, 48, and his 13-year-old sister Giselle Prosper and 16-year-old brother Kyle Prosper at the apartment the family shared in Luton, Bedfordshire, on September 13. He had also stabbed his brother more than 100 times.

The judge said Prosper had wanted to emulate and outdo atrocities around the world, including the massacre at Sandy Hook Elementary School in Connecticut in December 2012, when 26 people, mostly children were killed, and the mass shooting at Virginia Tech in April 2007 when 30 people were killed.

“Your ambition was notoriety,” she told Prosper, who had to be forced to come to the court to hear his fate.

“You wanted to be known posthumously as the world’s most famous school shooter of the 21st century.”

The judge said Prosper’s case featured many “recurrent themes” seen in school shootings around the world, including a sexual interest in children, a withdrawal into an online world, a lack of empathy towards victims and the selection of a “uniform” for the killings.

The court was told that Prosper, who had been unable to stay in education or hold down a job, had managed to forge a gun licence and used it to buy a shotgun and 100 cartridges from a legitimate firearms dealer the day before the murders.

His plan, the court was told, was to carry out a mass shooting at his old elementary school on Friday the 13th.

About 5am that day, Prosper carried out a test shot into a teddy bear in his bedroom.

His mother had woken first, realising something was “terribly wrong”. Prosper killed her, leaving a copy of the novel How to Kill Your Family on her legs, before shooting his sister as she hid under a table, and then stabbing and shooting his brother.

“The lives of your own mother and younger brother and sister were to be collateral damage on the way to fulfil your ambition,” the judge said.

With police swarming the area after the attack on his family was reported, Prosper flagged down police officers in a nearby street and showed them where he had hidden a loaded shotgun and 33 cartridges.

Bedfordshire Police Detective Superintendent Rob Hall read a statement on behalf of Prosper’s father Raymond Prosper, in which he said the deaths of his ex-partner Juliana and his son Kyle and daughter Giselle, had “much more meaning and importance”.

“Their deaths and the fast response of Bedfordshire Police stopped any other family in the community going through the pain we have suffered,” he said.