A diagnosis of autism alone does not increase the risk of a person committing a violent crime. The presence of other developmental disorders, including attention-deficit hyperactivity disorder (ADHD), may however explain why an association is sometimes seen between violence and autism.

In recent years, the number people diagnosed with autism spectrum disorder (ASD) has increased. However, the condition is very varied and many questions remain unanswered. What causes autism to develop for instance is still unclear. Similarly, little is known about what happens to people diagnosed with autism later in life.

Whether they are more likely to conduct violent crimes is a particular area of interest for researchers – especially since anecdotal evidence of this often receives widespread media attention and can negatively shape people's view of autism.

So far though, research on the subject has come up with conflicting results. A study now published in the journal of the American Academy of Child and Adolescent Psychiatry, is the largest to date to investigate this issue.

"A lot of the studies showing a link between autism and violence that have attracted media attention have been single case reports, or based on a small number of individuals," Dheeraj Rai, consultant senior lecturer in psychiatry at the University of Bristol, one of the study's authors, told IBTimes UK.

"There is a risk of such findings to be extrapolated to the entire population of autistic people, and to the emergence of false and stigmatising stereotypes. Our study included the entire population of Stockholm County and thus allows us to make conclusions at a population level."

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Are autistic people more at risk of committing violent crimes? iStock

ADHD and autism

The Stockholm Youth Cohort comprises 295,734 individuals whose medical data was recorded between 15 and 27 years of age. Of these, 5,739 individuals had a recorded autism diagnosis. Using the Swedish National Crime Register, the scientists looked at whether they had been convicted for violent crimes.

"'Violent crimes' included offences all the way from homicides and manslaughters to arson, assaults and robbery. Despite this wide grouping, violent crimes were rare in the population and we didn't have the statistical power to look at the risk for individual types of crime," Rai said.

Analysing the data, the researchers found out that individuals with autism, particularly those
without intellectual disability, initially appeared to have a higher risk of violent offending. However, when they took into account whether the individuals had been diagnosed with other developmental disorders such as ADHD and when they controlled for factors such parental criminal and psychiatric history and socioeconomic characteristics, this association became less robust.

In other words, although there was indeed a small proportion of people diagnosed with autism – between 4 and 5 percent – who were convicted for violent crimes, any relative increase in risk was explained by the co-occurrence of autism with other developmental disorders like ADHD.

In the future, taking into account the fact that ASD in an heterogeneous condition might be helpful to understand those who are more at risk of violent offending.

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Better managing ADHD in people with autism may help reduce the risk of them committing violent crimes. Istock

"This is a well-conducted study using unique Swedish population registries. It confirms the importance of considering co-occurring social and psychiatric risk markers when trying to prevent violent offending in general, and specifically among individuals with autism," said Niklas Långström, a violence researcher and professor of child and adolescent psychiatry at Uppsala University in Sweden, who was not involved in the present study.

"However, prior research and clinical experience suggest that lesser autism spectrum disorder severity as in Asperger syndrome might be related to higher violence risk. Hence, such a sub-analysis, if possible, would have been informative."

The study authors point out that improving our understanding and management of the other developmental disorders that can affect autistic people may potentially reduce any risk of them committing violent crimes.

"Co-occurring conditions like ADHD or mental health problems are commonly left unidentified in people with autism. There is not enough of a focus among clinical services in the UK to identify or manage these other conditions," Rai said.

"We need to start paying more attention and look at individuals with autism holistically, as early detection and management of such problems may not only improve their quality of life, but such supports may also potentially address the risk of violent offending."