Murder accused had intellectual age of 'nine-year-old' 

Jury hears suspect had borderline learning disability

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A warning that this story contains information which some readers may find distressing.

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A teenager accused of murdering a 14-year-old boy in Ramsey last year had the intellectual age of a nine-year-old.

That’s what a clinical psychologist told a murder trial at Douglas Courthouse today (14 October).

Fourteen-year-old Christopher McBurnie, from Castletown, died after being stabbed outside the defendant’s home on 29 May 2025.

A 15-year-old boy, who can’t be named for legal reasons, is standing trial accused of his murder.

Autism and ADHD

Doctor Rhiannon Lewis, a consultant clinical psychologist, was instructed by the defence to provide expert evidence in the case.

She assessed the defendant, who is now 15, in April this year – around 11 months after the fatal stabbing.

Dr Lewis had access to the teenager’s medical and mental health records, educational reports and material presented in the trial.

The jury heard the defendant was diagnosed with autism and ADHD, by the Isle of Man Child and Adolescent Mental Health Service, on 31 March 2025.

The referral to the service was made in November 2022.

Dr Lewis told jurors that it was her experience that there was ‘significant waiting lists for neurodevelopmental conditions’.

“Universally children have experienced longer waiting times post-Covid,” she added.  

WISC

Dr Lewis confirmed she agreed with the diagnoses and revealed she’d conducted her own cognitive function assessment using the Wechsler Intelligence Scale for Children or WISC.

It evaluates general intellectual ability in children and adolescents across five primary cognitive domains including verbal comprehension, fluid reasoning and processing speed.

“All of his scores fell in the extremely low range,” the doctor told the court.

The defendant scored in the bottom two percent of the population when measured against people of the same age from the general population.

This, Dr Lewis said, meant he was on the ‘borderline’ of being classed as having a learning disability.

“Cognitively, on this test, he was performing like a much younger child of nine years if you want to take an average,” the doctor added.

Dr Lewis confirmed the defendant’s ‘low-range intellectual capacity’ meant he was less able to compensate for his autism.

“I would consider him someone who’s very vulnerable with high support needs,” she added.

Social Isolation

The defendant, Dr Lewis said, had been ‘almost entirely isolated’ for at least 18 months prior to the incident and had avoided, and withdrawn from, school and lacked social interaction.

She confirmed that many children with autism prefer online communication adding that Covid-19, particularly, had forced the defendant’s generation online.

“There’s a pattern of over-reliance on online communication,” she added.

Dr Lewis had reviewed the messages exchanged on 28 and 28 May, over social media, between the defendant, Christopher and other teenagers in which the fatal fight was discussed.

She said the defendant’s messages were ‘restrictive and repetitive’ adding: “He did seem to find it difficult to disengage.”

The doctor also revealed the defendant had spent a lot of time playing an online computer game which featured ‘intense violence’ which was rated as ‘mature’ and for those aged 17 and older.

Risk Factors

Dr Lewis said the defendant’s ‘layering of problems’ stood out to her adding that he would have struggled in ‘high-pressured’ situations compared to the general population.

When asked how she thought the defendant would have presented if she’d assessed him at the time of the incident she said: “I’m fairly confident the performance would have looked worse.”

In cross-examination Prosecutor David Temkin KC asked Dr Lewis: “These conditions (autism and ADHD) – they don’t make a killer, do they?”

“No,” Dr Lewis replied.

‘Unhelpful Concept’

Prosecution expert Doctor John Marshall, a clinical and forensic psychologist, told the jury – via live video link – that he’d assessed the defendant in July this year.

He carried out his own autism and ADHD assessments confirming he agreed with the diagnoses made by CAMHS; he also conducted an IQ assessment.

Dr Marshall told jurors the service’s failure to assess the defendant’s intellectual ability, during his mental health assessment, was an ‘oversight’.

The psychologist also diagnosed the defendant with social anxiety disorder saying he was suffering with ‘chronic paranoid overthinking’.

The defendant was, the doctor said, ‘assuming others were judging him negatively’ adding this was ‘very common’ in boys with ADHD and autism.

Dr Marshall said he didn’t agree with Dr Lewis that applying a ‘mental age’ to the defendant was a helpful concept saying, instead, he’d rather use his IQ score.

He said the defendant was likely to have found it hard to take in, hold on to and reason with, information across most everyday situations.

“I take a view that cognitive deficits, such as this, are critical in someone’s functioning,” the doctor added.

The defendant’s overestimation of the number of people outside his home, on 29 May 2025, was a ‘well-recognised’ symptom of the conditions he was experiencing the doctor confirmed.

“Amplification under high stress would be common,” the doctor added.

“Autism and ADHD do not cause homicide or killing. If they did violence would be more prevalent in young people with these conditions.” – Dr John Marshall

‘Shut down’

Doctor Joanna Sales, a Child and Adolescent Psychiatrist, was also called to give evidence by the defence.

Having assessed the defendant she said it was her view that, in May 2025, he had ‘limited life skills’ and his world had ‘completely shut down’.

She explained that the teenager wasn’t going to school, wasn’t socialising, couldn’t leave the family home without support, couldn’t go to the shop or take public transport.

“He’d really missed out on a large part of normal teenage life,” she added.

Discussing the events of 29 May, which took place outside the defendant’s home, the doctor added: “He’s going to be a boy who can’t cope with what he’s seeing at the end of the garden path.

“His levels of anxiety would have been so sky-high he wouldn’t have been able to problem solve.

“He would have really struggled to understand what that group of people meant.”

 “His life had really, really, shut down.” – Dr Joanna Sales

Retrospectively

Doctor Richard Church, a child and adolescent psychiatrist instructed by the prosecution, told the court he also agreed with the defendant’s diagnoses.  

However, he told the court it would be ‘challenging’ to form a view ‘retrospectively’ of how the teenager would have been presenting in May last year.

He said he believed the defendant was ‘really quite isolated in many ways’ adding his social media interactions showed an ‘immature style of engagement’.

The defendant's messages, Dr Church said, displayed a lack of nuance, limited problem-solving and didn’t have a ‘moderating influence’ from others.

Discussing ‘online disinhibition’ – the loosening of social restraints and self-control when communicating digitally compared to face to face - he told the court: “It may be that he was somewhat more vulnerable than others to that.”

The Trial

The prosecution has now formally closed its case against the defendant.

The juvenile defendant denies the charge of murder.

The trial continues.