Floral tributes are left at the site of the Southport killings in 2024. (AP: Scott Heppell)

A mass killing by a British teenager who fatally stabbed three girls and seriously wounded 10 other people at a Taylor Swift-themed dance class in 2024 “could and should have been prevented” if his parents and state agencies had acted as his well-known fixation on violence escalated, according to a report.

Adrian Fulford, a retired judge who led a nine-week inquiry into the attack, issued a 763-page report on Monday, local time, cataloguing the many times parents or authorities could have intervened in Axel Rudakubana’s life to ultimately prevent him from carrying out killings.

Mr Fulford said the killings were unprecedented in the UK for their “extreme and very particular depravity”.

“One of the most striking conclusions from this inquiry’s extensive investigation is the sheer number of missed opportunities over many years to intervene meaningfully, which directly contributed to the failure to avert this disaster,” he said.

“The consequences were catastrophic.”

Elsie Dot Stancombe, 7, Bebe King, 6, and Alice da Silva Aguiar, 9, were killed in the stabbing attack. (Supplied)

Rudakubana, who was 17 when he carried out the attack, is serving a life sentence with no chance of parole for 52 years for killing Alice da Silva Aguiar, nine, Elsie Dot Stancombe, seven, and Bebe King, six, and wounding eight other children and two adults.

The attack at Southport in north-western England triggered days of disorder, after far-right activists seized on incorrect reports that the attacker was a Muslim migrant who had recently arrived in the UK.

Rudakubana was born in Wales to Rwandan Christian parents.

The report made 67 recommendations to prevent similar atrocities.

Prime Minister Keir Starmer has promised changes to correct the “systematic failures that led to this terrible event”.

“The report today is truly harrowing and profoundly disturbing,” Mr Starmer said.

“While nothing will ever bring these three little girls back, I’m determined to make the fundamental changes needed to keep the public safe.”

Police, social workers and educators were well aware of problems with Rudakubana.

In 2019, aged 13, he was convicted of assaulting another child at school with a hockey stick and placed under the supervision of a local service for youth offenders.

He was referred to the government’s anti-extremism program, Prevent, three times between 2019 and 2021 for expressing interest in school shootings, the 2017 London Bridge attack, the Irish Republican Army and the Middle East.

Adrian Fulford, a retired judge who led the nine-week inquiry into the attack, has issued a 763-page report. (AP: Peter Byrne/PA via AP)

Each time, the case was closed because he was not considered susceptible to becoming a terrorist.

During that same period, police were called to his home five times over unspecified concerns about his behaviour.

Rudakubana was given mental health and educational support, but later appeared to have stopped engaging with social workers.

He was expelled after taking a knife to school and rarely attended a subsequent school.

“Far too often, AR’s ‘case’ was passed from one public sector agency to another in an inappropriate merry-go-round of referrals, assessments, case-closures and ‘hand-offs,’” said Mr Fulford, who only used the killer’s initials.

Mr Fulford highlighted an incident in March 2022 when Rudakubana was caught on a bus with a knife, told police he wanted to stab someone and admitted trying to make poison.

That should have sparked an arrest that would likely have led to a search of his house and the discovery of seeds he had bought to make biological toxin ricin and terrorist material downloaded on his computer, Mr Fulford said.

Rudakubana was not arrested and was released to his parents, who feared him and repeatedly failed to report the various knives he had purchased, his troubling behaviour and threats he had made.

While Mr Fulford outlined several failings by Rudakubana’s parents that could have prevented the tragedy, he said they should not be vilified for what had become a challenging situation.

“Their life at home must have become little short of a nightmare given, to use the words of his own father, AR had turned into a ‘monster’,”

Mr Fulford said.

Following the Southport attack, police searched Rudakubana’s home and discovered ricin hidden under his bed and a downloaded document, which was described as an Al Qaeda training manual.

Police concluded that his crimes should not be classed as terrorism because he had no discernible political or religious cause or motivation.

Home Secretary Shabana Mahmood said new legislation would be introduced to address violent plots that were not considered terrorism.

“Unlike terrorist attacks, if you are planning an attack without an underlying ideology, there is no crime on the statute book,” Ms Mahmood said.