Making a Murderer: 21 Patterns of Behaviour Found in Serial Killers

What really makes a murderer? In this article we take a look at some of the early behavioural patterns that have been identified in serial killers, and have a think about how these might help us to create the monsters in our stories!


The Homicide Triad

When talking about early indicators of murderers, you may be familiar with the term ‘homicide triad’: three early behavioural indicators of a serial killer. It may also be described as the ‘triad of sociopathy’, the ’triad of evil’ or ‘the Macdonald triad’ after its founder, psychologist J.M.Macdonald in 1963.

And what are these three indicators?

Pyromania is linked with both aggression and sexual arousal for a would-be serial killer. If we consider that a pyromaniac takes great pleasure from destroying a property with fire, it is not too strong a leap to imagine the similarities that person will feel when destroying a life. Pyromania is therefore often an early indicator of serial murder.

Torturing animals is thought to be a ‘practice run’ for the evolving murderer. In fact studies have shown that when murders move on from animals to humans, they retain a similar method of torture. Animals such as domesticated household pets tend not to retaliate and are easy to source, and so help the torturer build their confidence to carry out the act on a human victim.

Bedwetting (also known as ‘enuresis’) which continues after the age of five is also an indicator of future violence.

What these have in common is an early experience of childhood abuse and/or humiliation leading to outward aggression. Macdonald’s theory has been criticised as oversimplifying the number of violence indicators. For example pyromania, torture of animals and bedwetting are also common by-products of children who have been abused; many of whom do not go on to commit murder.

Macdonald’s theory also lacks empirical evidence, having failed later clinical tests where no positive correlation could be found between the triad and convicted offenders.

Given then, that the homicide triad may not be the scientifically sound route to go down to flesh out the background of a murderous character, what other theories of serial killer behaviours exist?


Norris’s 21 Patterns of Behaviour

In 1988 psychologist Joel Norris conducted interviews with over a dozen serial killers, their families, psychiatrists and other medical professionals in an effort to better understand the ‘disease’ of serial murder. He developed 21 ‘red flags’ that could indicate a person who is pre-disposed to episodic violence and criminal activity:


1. Ritualistic behaviour

This will be a repeated, observable pattern that the criminal cannot change. For example, a particular burial method, weapon, method of ‘posing’ the body or taking of a personal item from the scene.


2. Masks of sanity concealing mental instability

The murderer is able to outwardly display normal socially acceptable behaviour despite the urge to kill, almost as though they have a split personality.


3. Compulsivity

One or more aspects of the killer will be compulsive in nature, for example, a compulsively neat appearance, cleanliness, record keeping or cataloguing of victim photos and paraphernalia.


4. Periodic search for help

The murderer may reach out for help before they get past the point of no return.


5. Severe memory disorders and a chronic inability to tell the truth

A serial killer is often a pathological liar, in part because they are constantly hiding their dark secret from the public.


6. Suicidal tendencies

Many serial killers kill themselves once caught, or if not caught for a long time and their self-hatred gets the better of them.


7. History of committing assault

The murderer is often ‘practised’ at violence before committing to the kill.


8. Hypersexuality and abnormal sexual behaviour

This is often a result of severe childhood abuse. Hypersexuality refers to a sexual desire that can never be satisfied; the killer cannot find a release.


9. Head injuries; injuries suffered at birth

Head trauma at birth or in early childhood is a common pattern among known serial killers. Head trauma can cause seizures, hallucinations and delusions. Repeated head injury is a particularly strong indicator that a person may become very violent.


10. History of chronic drug or alcohol abuse

Dependency on drugs and alcohol can suppress normal social controls and reveal primitive behaviours like aggression and violence.


11. Parents with a history of chronic drug or alcohol abuse

Some killers were born with drug dependencies as a result of having drug-dependent parents. Some parents may irresponsibly introduce their children to drink and drugs far too early.


12. Victims of childhood physical or mental abuse

‘Child abuse begets abuse’; sadly, being abused as a child very often leads to the abused becoming the abuser. Such severe trauma at a young age means serial killers barely had a chance at a normal life.


13. Result of unwanted pregnancy

If the parent punishes the child for being born, we’re looking at an unhappy home life and possibilities of abuse.


14. Product of a difficult gestation for mother

Perhaps due to complications with drink/drugs or from being extremely poor. Extreme anxiety or tension during pregnancy could lead to severe developmental problems for the baby.


15. Unhappiness in childhood resulted in inability to find happiness

A child may simply never learn how to be happy, may be left out of things by others. As a result, they may be unable to feel pleasure in adult life.


16. Extraordinary cruelty to animals

Household pets are especially in danger and may be hurt for the pleasure of it.


17. Attraction to arson without homicidal interest

Fire setting can give the killer a sense of control where they otherwise do not; after adolescence, this control may be obtained through the act of murder and the killer could ‘grow out of’ arson.


18. Symptoms of neurological impairment

Norris lists 22 impairments which have been linked to known serial killers. If present in an individual after adolescence, these could be a ‘red flag’:

Dyslexia, problems with directions/maths/reading, hypergraphia, grandiosity, hypervigilance, hypersexuality, hyposexuality, hyperreligiosity, visual or auditory hallucinations, rambly or illogical thought processes, paranoia or chronic feelings of persecution, isolation, alienation or withdrawal, chronic depression and crying, incontinence, sleep disorders, difficulty with spatial coordination and perception, poor muscular coordination, history of seizures, chronic headaches, lability of moods or animal-like body movements.


19. Evidence of genetic disorder

Abnormalities as a result of faulty genetics may indicate a serial killer, e.g.:

Bulbous fingertips, wiry or very fine hair, large head circumference, epicanthus, hyperteliorism, low-seated/malformed/asymmetrical/very soft ears, teeth abnormalities, a third toe longer than the second or a speckled tongue.


20. Biochemical symptoms

An inability to get rid of toxins may contribute to episodic violence.


21. Feelings of powerlessness or inadequacy

Killing temporarily helps the serial murderer gain control, hence why other indicators include arson and cruelty to animals. This trait can emerge at adolescence as the killer starts to exercise their power; the outcome of this display of power is greatly affected by how those in positions of authority respond to it. For example is the adolescent is laughed at or put down, things could end badly.


How to use this list as a writer?

This list of behaviours could help you establish a background for the killer in your crime story. Have a think about the following questions:

What happened in your killer’s childhood?

Are there standout events? What are his/her ‘stressors’?

What is the family’s medical history? What is the killer’s family like and how might they have helped or hindered him/her?

What was the inciting event that led to the first kill?

How might employment contribute to the killer’s need to be violent? For example, does their job make them feel powerless? Does it lead to them telling a lie they cannot undo?

Which of these behaviours might be hinted at by the way the crime scene is left?


Over to you

Do you think these theories still hold up today? Have they helped you think of some ways you might develop your character’s stories? Let me know in the comments!

Leave me a reply!