The #1 Question about Serial Killers

The question I’m asked most often has no easy answer.

Posted Mar 12, 2018

K. Ramsland
Source: K. Ramsland

Due to my area of expertise, nearly every week I receive queries from students (and sometimes reporters) asking me questions like, can I spot a serial killer? What turns someone into a serial killer? What sets serial killers apart from everyone else? Can they be cured?

The number one question concerns nature vs. nurture, as recently asked in this form, “Do you think life experiences contribute to making a person into a serial killer or is it more about genetics?”

It’s difficult to address such a query because it contains three erroneous assumptions, notably that:

 1) “serial killer” is a distinct type of criminal category such that these offenders share multiple distinct personality, motivational and behavioral similarities;
 2) we can calculate the ratio between the influence of nature vs. nurture for offenders within this category; and
 3) knowing this formula will allow us to understand, identify, cure, or stop them.

I’ve written about the broader myths about serial murder here, but let’s dissect these three notions.

First, what identifies someone as a serial killer is a specific behavior: having killed two or more victims in at least two incidents ( No other personality or behavioral characteristic places all serial killers into a criminological category. Although some subgroups have core behaviors in common, there is actually a great deal of variation in this population, from a range of motives, backgrounds, ages, and behaviors, to differences in physiology, mental state, and perceptions that influence reasoning and decisions.

Among the approaches, I use in my college course on serial murder to address nature vs. nurture is a flexible theory proposed by neuropsychologist Debra Niehoff. She has reviewed the most significant literature about the interplay of genes and the environment in the development of violent behavior, and she finds that each factor modifies the other throughout a person's lifespan. “The brain perceives and interprets,” she says, “but the biochemical alterations triggered by experience continually update this circuitry, shaping worldview in accordance with conditions” (2003).

This gets more complex when we add individuality. Each person uniquely processes a given situation, they process it differently at different ages and in different circumstances, and some gravitate toward violence. This can be defensive violence or aggressive, psychotic or psychopathic, reactive or predatory, to name some possibilities. 

“Building on the template constructed during the early years of life, the child uses these new relationships as a test laboratory in which to examine the validity of the worldview imprinted in the brain by interaction within the home environment, adding new information to refine the existing impression of the world as a safe or hostile place” (Niehoff, 2003).

Any factor—abuse, neglect, physical deformity, deviance, bullying—might have different influences on different people, and new experiences can modify perceptions positively or negatively. One factor might have more influence on subject A than on subject B.  Or, this factor might have more influence on subject A as a youth than as an adult. One person with a brain abnormality might become violent, but others who have the same condition might not, and others with no such condition might turn to violence for other reasons.

How each person sorts it out and manages his or her situation depends on a unique interplay of external and internal factors.

It’s complicated!

A person’s brain, Niehoff says, tracks his or her experiences through chemical codes and makes habitual associations with the past. Every experience involves dedicated chemicals that influence and control emotions, moods, and reactions, such that our feelings derive from the sum of many diverse chemical and physiological states. Each environmental interaction gets handled via a specific “neurochemical profile,” which is influenced by attitudes that derive from an array of encounters and experiences. These will change with age and exposure.

In some cases, the condition of the brain plays a strong role. Dr. Adriane Raine found brain deficits in violent individuals—specifically in areas of the limbic system (emotional center) and the prefrontal cortex. These deficits might influence certain people to be impulsive, fearless, less responsive to aversive stimulation, and less able to make appropriate decisions about aggression toward others.

Or… they might not.

Let’s add the influence of a particular historico-cultural context. In medieval France, for a dramatic example, when the witch-finders hunted down “werewolves” as Satan’s spawn, the emphasis on bestial behavior could affect a mentally unstable person. Some became particularly vicious killers, using their teeth to bite victims in a wolf-like manner.  

In other words, for any given serial killer, we can't determine how much of their criminal development is due to something in their physiology vs. something from their environment. We know it’s both, but we cannot precisely calculate which has more influence.

In that case, we also don’t know if an ability to calculate this ratio will be particularly meaningful. We hope it will be, and those in neurocriminology and neuropsychology have such goals. However, definite answers to these questions are still in the future.

So, to sum it up: you can’t necessarily spot a serial killer, we don’t yet know an exact formula for nature vs. nurture, and each offender’s behavior and potential response to treatment will depend on the specific criminogenic factors in his or her development.

That's why I cannot give students a simple answer to their number one question.  


Raine, A. (2013) The anatomy of violence: The biological roots of crime. New York, NY: Pantheon Books.

Niehoff, D. (2003). A vicious circle: The neurobiological foundations of violent behavior. Modern Psychoanalysis, 28(2), 235-245.

Niehoff, D. (1999). The biology of violence: How understanding the brain, behavior, and

environment can break the vicious circle of aggression. New York, NY: The Free Press.

Ramsland, K. (2005). The human predator: A historical chronicle of serial murder and

forensic investigation. New York, NY: Berkley.

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