Teenage killer who murdered his mother and younger siblings was banned from twisted website where people go to watch others die

He was arrested shortly afterwards while armed with a shotgun near St Joseph's Catholic Primary School.

Hours before the murders, Prosper recorded a chilling 70-second video threatening his sister over a video game.

Wearing a yellow bucket hat and black T-shirt, he calmly declared he would take violent revenge against Giselle for making "incorrect choices" in The Walking Dead game.

In the video, filmed at their Luton flat, Prosper said his sister's "face will be mutilated further than necessary," claiming he was "chosen" to protect a fictional character called Clementine in the zombie game.

Police were alerted at 5:30am on September 13 after a neighbour heard screams from the family's flat.

Officers discovered the bodies of Prosper's three victims, who had been shot in the head during the night.

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Prosper had fled the scene but was quickly found by police lurking in nearby Bramingham Road where officers discovered he had hidden a loaded shotgun in bushes and found him with more than 30 cartridges and a kitchen knife.

An investigation later revealed substantial evidence that Prosper had been planning a mass shooting at St Joseph's Catholic Primary School, where he and his siblings had once been pupils.

Prosper's online behaviour revealed a disturbing obsession with extreme violence and child abuse.

He was banned from a gore website after repeatedly "sexualising minors", with one moderator telling The Daily Mail his comments supported "child-adult sexual interactions."

In another video, he sarcastically suggested child abuse was blamed for "virtually every mental disorder."

Neighbours revealed Prosper spent so much time in his bedroom that they were unaware he existed, despite being on friendly terms with his mother and siblings.

Police discovered he had spent months fixating on extreme violence and other school shootings, including the Sandy Hook massacre.

Detective Chief Inspector Sam Khanna called it "a truly tragic and shocking case" where "three innocent members of the same family have been brutally killed by their son and brother."

Assistant Chief Constable John Murphy said officers had prevented Prosper "from going through with his plans to target a school."

St Joseph's headteacher Maureen Murphy said: "We were devastated to learn of the tragic death of our former students Kyle and Giselle and their mother Juliana."

She added that while they were "very shocked" to learn the school was targeted, there was "no threat to the school."

Speaking on LBC, Home Secretary Yvette Cooper described it as "the most devastating crime," saying it raised "wider issues about young people becoming obsessed with violence" and the "school massacre issue."

Cooper revealed that following the Southport attack, the government had begun examining reforms around the Prevent programme.

She added they were "looking at what more needs to be done" about violent, fixated teenagers and highlighted "serious issues about what young people see online."

Luton Council leader Hazel Simmons said the revelation about planned school violence was "extremely shocking, distressing and upsetting," and acknowledged the emotional impact on "children, staff, parents and carers across our school community."

The council will ask schools to review their security measures following the court revelations.

Prosper, who was remanded in custody ahead of sentencing next week, showed no emotion during his six-minute court hearing, where he admitted three murder charges and firearms offences.

At a previous hearing, his estranged father Ray Prosper had called out: "I still love you, son. It's not your fault, OK?"