What do famed serial killers Ted Bundy, John Wayne Gacy, and TV killer Dexter have in common? Besides killing an incredible amount of people — the first two have killed as many as 70 each — all three of them had issues with neurodevelopmental and psychosocial issues. Both Bundy and Gacy were diagnosed with antisocial personality disorder and Dexter experienced the extremely graphic, bloody murder of his mom. A new study finds that these issues are among a group of indicators that someone may become a serial killer.

Antisocial personality disorder is characterized by a person’s inability to distinguish between right and wrong. Their perception of situations and relating to others is dysfunctional, and they often manipulate people and act with indifference. In the same way that people with the disorder may be removed from the social norm, those with autism spectrum disorder (ASD); who experienced a head injury; or who have had some sort of psychosocial stressor in the past, may also become removed, putting them in a mental state capable of committing mass crime, according to the study from the University of Glasgow.

When Adam Lanza, the man behind the Sandy Hook shootings, was 13, he was diagnosed with Asperger’s syndrome, a form of ASD. Common signs of the condition include shyness, the inability to empathize, and speaking in a monotonous tone, and Lanza was all of these. Still, the researchers emphasized that none of these disorders implicate that someone is a serial killer.

“It is crucial to note that we are not trying to suggest that individuals with ASD or previous head trauma are more likely to be serial killers or commit serious crime,” said lead researcher, Dr. Clare Allely, from the Institute of Wellbeing at the university, in a press release. “Rather, we are suggesting that there may be a subgroup of individuals within these groups who may be more likely to commit serious crimes when exposed to certain psychosocial stressors.”

Allely’s team discovered this connection after searching popular databases for correlations. Their search terms included “autism and serial killer,” “psychopathy and autism,” “murder and autism,” and “brain injury and serial killer.” They also looked at books, studies, and electronic documents, finding a total of 239 eligible killers, the Daily Mail reported. Of these, 28 percent had ASD, 21 percent had suffered a “definite or suspected head injury in the past,” and 55 percent had gone through some sort of psychosocial stressor.

The research provides authorities with a bit more insight into what possesses people to commit mass murders. Nevertheless, the research is still very much “in its infancy,” Allely said, and gives authorities more of a reason to investigate future killers’ backgrounds for such traumas and neurodevelopmental disorders.

“This is a very serious issue, and research like this is vital if we are to develop preventive strategies,” Carol Povey, director of the UK’s National Autism Society Centre for Autism, told the Daily Mail. “But we would urge people not to jump to conclusions about people with autism, and to make judgements about a whole section of society. This research reaffirms the importance of ensuring that people with autism get the support they need as early as possible.”

Source: Allely C, Minnis H, Thompson L, Wilson P, Gillberg C. Neurodevelopmental and psychosocial risk factors in serial killers and mass murderers. Aggression and Violent Behavior. 2014.