McDonald Triad paper: sample of 100
The 1963 McDonald Triad paper was based on just 100 psychiatric patients — none of whom had actually committed violence; they had only threatened it.
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Episode 671: Gary Ridgway : Redux Part I - Wrong Way Gary
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Jul 3, 2026
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The McDonald Triad: Fire, Animals, and What It Actually Means
At 32:44 · chapter starts 29:20
Starting in second grade, Gary Ridgway set his own garage on fire, then began setting neighboring garages ablaze and running when he heard sirens. He also suffocated his own cat by locking it in a cooler. Marcus uses this moment to explain the McDonald Triad — the behavioral triplet of bed-wetting, fire-starting, and animal cruelty widely used as a serial killer indicator — and its actual origins: a 1963 paper by forensic psychiatrist John McDonald based on just 100 psychiatric patients who had only threatened violence, never committed it. [1] — Marcus Parks "The McDonald Triad — bed-wetting, fire-starting, animal cruelty — was never designed to predict serial killers. The 1963 paper studied only…" 31:10 The FBI's Behavioral Science Unit ran with it far beyond what McDonald intended. A 2018 re-analysis reframed the triad as a reliable indicator of childhood abuse. Marcus then discloses that he personally hit all three points as a child, using his own experience to argue that the triad describes traumatic environments, not future killers — and that Gary Ridgway's failure to seek therapy is the key divergence.
The McDonald Triad: Abuse Detector, Not Killer Predictor
The McDonald Triad — bed-wetting, fire-starting, animal cruelty — was never designed to predict serial killers. The 1963 paper studied only 100 psychiatric patients who had threatened, not committed, violence. A 2018 re-analysis found the triad is actually a reliable indicator of severe childhood abuse, which is why Marcus Parks himself hit every point.
McDonald Triad reframed as abuse indicator (2018)
In 2018, authors Charlotte Parfitt and Emma Aileen re-examined the McDonald Triad and found it is not a predictor of serial killing but is a strong indicator of childhood abuse.
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