There’s no specific trait or source of a serial killer. In fact, it’s best said by the FBI themselves. “There is no single identifiable cause or factor that leads to the development of a serial killer. Rather, there are a multitude of factors that contribute to their development.” However, there is a chain of signs and common patterns that can be used to link them together. 

Most theories about how a person is ‘formed’ comes from the Nature Versus Nurture argument in psychology. This argument differs between whether or not people are defined by their genes and biology, or are a product of their environment and childhood experiences. This applies to serial killers, too. Looking into both genes and telltale signs from their childhood can give away a glimpse of what makes a murderer. 

Firstly, looking at the nurture side of the argument, the common factors found in most serial killers’ childhoods are usually being separated from their mothers shortly after birth, absent parents, physical or sexual abuse and/or being seen as a loner or social reject early on. The infamous Ted Bundy experienced many of these. Despite his insistence on his ‘picture perfect’ childhood. Most notably, according to Conversations With A Killer: The Ted Bundy Tapes on Netflix, Bundy was separated from his mother shortly after birth – having been born and left in a home for unwed mothers where he stayed until his grandfather demanded his mother bring him home . Many people believe close contact with mothers after birth is crucial for proper development in children, and a lack of this is what could have been the beginning of Bundy’s problems. Additionally, Bundy may have experienced physical abuse from his grandfather as a product of the man’s ‘uncontrollable rage,’ had an absent father and a tense relationship with his stepfather, exhibited attempts of physical violence himself, and was known as a peeping tom and shoplifter early on. 

The childhood of a serial killer is highly valued when evaluating them. After all, “(…) serial murderers, like all human beings, are the product of their heredity, their upbringing and the choices they make throughout development,”  according to the FBI in Serial Murder: Multi-Disceplenary Perspectives for Investigators. Childhood is where foundations are laid for a child’s perspectives on truths about the world. Should a person have an unstable or twisted foundation that they fail to unlearn, it creates a setup for perceiving an equally unstable world in which a terrible action might be justified. Essentially, different childhood experiences create different traumas which could be potential motivations for different types of killers.

On the other hand, we can examine the nature side of the argument by focusing on whether or not genes play a role in becoming a serial killer. Certain chemicals could increase impulsivity and violent behaviors which put one at risk for enacting further violent behaviors. Specifically focusing on the Monoamine Oxidase A. gene, which helps break down neurotransmitters like serotonin and help regulate mood, a defective or low amount of MAOA genes paired with a low amount of dopamine can create aggressive behavior. In a rare case, a Dutch family had a complete deficiency in the MAOA gene and generationally repeated violent criminal behavior. Still, this loops back to nurture rather than nature, considering not every person with increased aggression in general would become a murderer. However, if they are subjected to a traumatic childhood as well, their percentage of risk kicks up even higher.

A secondary example of genes affecting a person’s chance of becoming a serial killer is found when Professor James Fallon, American neuroscientist and professor at the University of California, blindly analyzed different brain scans in a 2005 study. Fallon was asked to examine different PET scans to find anatomical patterns of the brain that might be associated with psychopathic tendencies of people. 

“I was looking at many scans, scans of murderers mixed in with schizophrenics, depressives and other, normal brains,” Fallon said. He managed to differentiate between the many killers’ scans and other PET scans – namely due to the damage to the orbital cortex and the temporal cortex, specifically the amygdala. The amygdala, which houses and controls animal drives, fear, aggression, impulsivity and other intense emotions, may explain why murderers could be driven to extreme behavior and hostility. In other words, it could be correlated with the urge to kill. 

Whether or not damage to the brain is enough to warrant such a violent reaction is at question, but ultimately it is genes paired with environmental factors that create a serial killer and a drive large enough to enact these urges in a person. This could mark the beginnings for a signature brain profile of a serial killer and should be another common factor considered in the development of serial killers. 

Nevertheless, people don’t just wake up and choose to kill. Triggers, typically stressful situations, are usually needed to drive someone to commit a crime, which is the true final step to becoming a murderer. Ultimately, nothing truly makes a person a killer until they kill someone.