Halloween Special: the psychology of serial killers


2020 has been a year of crime obsession. Locked away in our rooms, we all turned to Netflix’s crime documentaries, hoping that serial killers were also staying inside. But what makes a serial killer? Is there a special blend of psychopathy, trauma and opportunity that guarantees a murder? Is serial killing down to the individual’s genetic makeup, or is it a product of an unstable environment?

I’ll try to answer your questions.

A serial killer is defined by professionals as an individual who kills more than three other people within the space of a month, with a ‘cooling off’ period between murders (which separates them from spree killers and mass murderers). Scientifically, they are grouped into four broad categories: mission-oriented (who kill a certain group for violating certain values), visionary (who report hearing voices urging them to kill), power-control (who derive sexual pleasure from the power they exert over their victim) and hedonistic killers (who kill for personal gain, gratification or thrill).

However, there is some amount of overlap in both psychological make-up and behaviour between groups, meaning that categorising a specific killer is often not as clear cut as that.

Furthermore, there seem to be overarching psychological factors that are reported in the vast majority of serial killer case studies, revolving round physical, emotional or sexual abuse in childhood.

Most serial killers have a lower-than-average IQ

Hickey’s trauma control model explained that early childhood trauma or a negative childhood environment is the main contributing factor for the development of homicidal behaviour later in life. Peter Vronsky theorizes that abuse may cause a level of psychological underdevelopment later in life, where primal instincts to kill for survival are left unmoderated, due to a lack of decent parenting and socialization in early life.

When viewing this in conjunction with the diathesis-stress model of abnormal psychology (the idea that we all have an individual predispositional protective resistance to traumatic stress, but once the stress level surpasses the diathesis level, a disorder develops), the suggestion is that, potentially, we are all one traumatic event away from serial murder.

Adolescence also seems to be a critical period in the development of a serial killer. Formative serial killer experiences involve the McDonald triad in teenage-hood. As opposed to the McDonald triad of my own youth (a Big Mac, medium fries, and coke), this triad involves bedwetting into the early teens, sadism, and pyromancy.

In addition, most serial killers have a lower-than- average IQ (a study found the mean of 202 serial murderers intelligence test scores was 89). Partner these factors with the natural cruelty of teens and it is near certain that adolescents who go on to become serial killers would have been ridiculed by their peers – further inhibiting socialisation and the development of empathy.

As opposed to the McDonald triad of my own youth (a Big Mac, medium fries, and coke), this triad involves bedwetting, sadism, and pyromancy.

That being said, there are still notable serial killer exceptions, who had neither a traumatic nor abusive youth. Harold Shipman, a British GP who killed
approximately 250 people, had neither a tumultuous upbringing nor a low IQ.

Jeffrey Dahmer, potentially the most famous American murderer, had an ordinary childhood, marred only by his parent’s amicable divorce when Dahmer was in high school. Still, a few weeks after his school graduation, he committed his first murder, and subsequently killed 16 more gay men across the US.

There is no equation that can reliably calculate the likelihood of an individual committing multiple homicides based on the size of different environmental and genetic influences.

Researchers in this field face the dual conundrum of serial killers being (thankfully) very rare, and the difficult task of operationalizing psychological
factors into workable experimental variables. In all likelihood, serial killers are probably created in a highly individualistic manner – through a web of interdependent nature and nurture factors.

Image: HannahJoe7 from Pixabay

Leave a Reply

Your email address will not be published.


This site uses Akismet to reduce spam. Learn how your comment data is processed.