Forensic Psychiatry, McDonald’s Triad and Serial Killer

“Together or alone, the triad behaviours can indicate a stressed child with poor coping mechanisms or a developmental disability; such a child needs guidance and attention. However, until we design and carry out better empirical studies than we’ve seen thus far, researchers and media agencies should refrain from stating that the triad identifies a future serial killer.”

Katherine Ramsland, Psychology Today

Forensic Psychiatry is a branch of psychiatry where the medical and the legal worlds overlap. It involves application of medical psychiatric expertise in legal contexts.

'On your personals AD, you say you're a butcher . . . that's fascinating. Tell me about that . . .'

John Macdonald was a forensic psychiatrist, who after some research came to conclusion that if set of three behaviours i.e. obsession with fire setting, cruelty to animals and persistent bedwetting were exhibited by child (all three or any combination of two) then it was predictive of or associated with later violent tendencies esp. those related to serial offences. These three set of behaviours were called Macdonald’s Triad.


He first proposed this triad in published paper titled “The Threat to Kill”.

Macdonald came to this conclusion based on research done by comparing 48 psychotic patients with 52 non-psychotic patients who all had threatened to kill someone (they threaten to kill but did not actually commit crime)

Later some more research was carried on McDonald’s Triad. But since research group was small and unrepresentative, study lacks reliability and hence its predictive value is questionable.

“An extensive review of the literature reveals little empirical support for the validity of this triad. The fact that the Macdonald triad has been and continues to be presented as fact suggests a need to revisit the process by which theories of violent behaviour are derived and sustained.”

-Kori Ryan, author of The Macdonald Triad: Predictor of Violence Or Urban Myth?

But some criminologists have applied the triad to various offender populations, especially serial killers. They found that violent offenders do have excessive fire-setting, animal cruelty, or bedwetting past age five in their backgrounds, but rarely do all three behaviours show up.

Fire setting is result of extensive periods of humiliation suffered by several adult serial killers during childhood. These repetitive episodes of humiliation can lead to feelings of frustration and anger, and gets released in form of fire setting.

'I wanted to set the world on fire. I never dreamed I'd be charged with arson.'

Some offenders kill animals as a rehearsal for killing human victims. Cruelty to animals is mainly used to vent frustration and anger the same way fire setting is. During childhood, serial killers could not retaliate towards those who caused them humiliation, so they chose animals because animals were viewed as weak and vulnerable.

'How many times has Mum told you not to be cruel to dumb animals?'

Persistent bed-wetting beyond the age of five ( called as Enuresis) can be humiliating for a child, especially if he or she is belittled by a parental figure or other adult as a result, this could cause the child to use fire setting or cruelty to animals as an outlet for his or her frustration.

'Is there anything worse than waking and going to the bathroom?'

The triad behaviours are not causal when examining a relationship with later predatory behaviour, but rather, are predictive of an increased likelihood of the future behaviour patterns.



Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s