A 19-year-old man who shot dead his mother and two younger siblings at their home in Luton was also plotting a shooting at his former primary school, according to police.

Nicholas Prosper admitted murdering Juliana Falcon, 48, Kyle Prosper, 16, and Giselle Prosper, 13, when he appeared at Luton crown court on Monday.

He also admitted other offences including buying a shotgun without a certificate, possession of a shotgun with intent to endanger life and possession of a kitchen knife in a public place.

Prosper had also planned to commit a shooting at St Joseph’s Catholic primary school in Luton, where he and his siblings had been pupils. Its headteacher, Maureen Murphy, said staff were “very shocked” to learn of the plan, but that there was no threat to the school.

Prosper was apprehended by officers before he could carry out his plans, Bedfordshire police said. A loaded shotgun with more than 30 cartridges was found hidden in a bush after his arrest.

Details of Prosper’s plot comes after it was revealed that the Southport killer, Axel Rudakubana, had also been suspected of planning to target a school.

Prosper murdered his family in a “cold-blooded attack” with a shotgun he obtained without a licence, said Chris Derrick, a deputy chief crown prosecutor at the Crown Prosecution Service.

Officers were called to the family’s flat in Leabank in Luton at 5.30am on 13 September 2024 after reports of gunfire. His mother, brother and sister were found dead from gunshot wounds to the head. The perpetrator and victims all lived in the same house.

DCI Sam Khanna, from the Bedfordshire, Cambridgeshire and Hertfordshire major crime unit, said: “This was a truly tragic and shocking case in which three innocent members of the same family have been brutally killed by their son and brother.

“No words can fully describe the tragedy their loved ones have experienced, and our thoughts continue to be with them at this difficult time. We are pleased that Prosper has pleaded guilty and will not put his family through the pain of a trial, and that he will soon face a significant jail sentence.

“What was subsequently uncovered during our investigation left no doubt as to his intentions to carry out an attack at a school, but fortunately Prosper was apprehended before he could cause any further harm.”

Speaking outside court, he added that discovering that Prosper had planned to attack a school “left our whole investigation team in shock and disbelief”.

“We cannot ever begin to comprehend why someone would plan to kill innocent children and are so grateful to those arresting officers who helped prevent this from taking place.”

Assistant chief constable John Murphy of Bedfordshire police said Prosper had intended to cause “maximum harm and distress” to the wider community. “We understand the deep shock this case will have on people within Luton and across the country,” he said.

“We are working closely alongside Luton borough council to engage with schools in Luton to provide support, assistance and guidance to both schools and parents.”

Hazel Simmons, the leader of Luton council, said the council would ask schools to review security measures.

“The revelation that the perpetrator had plans to cause further harm in one of our schools is extremely shocking, distressing and upsetting, and we don’t underestimate the emotional difficulty this news will have on children, staff, parents and carers across our school community.

“Our schools have robust systems in place to keep children safe, and security is constantly reviewed and monitored. Just recently we asked our schools to further review security and for increased vigilance following the incident in a school in Sheffield.

“We will be asking schools to further review security measures in light of what came out in court today.”

Det Supt Rob Hall, from the region’s major crime unit, previously said officers who arrived at the scene were “met with such awful circumstances”.

Falcon was described as a “strong, loving mother,” who put others first, in a family tribute last September. The family said Kyle was “a kind and funny young man” and Giselle was “lovable with an infectious smile”.

Last September, when Prosper first appeared in court, the public gallery was full of family members, many of whom were tearful and shook their heads during his short appearance in the dock.

Prosper, whose sentencing will take place on 5 March, was remanded into custody.