Crime Library: Criminal Minds and Methods

What Makes Serial Killers Tick?

Natural Born Killers I

Genetics/Bad Seeds Are the psychopathic criminals really different from birth? Many parents say that their children who grow up to be violent offenders are markedly different from their non-violent siblings. Three-year-old Ted Bundy sneaked into his teenage aunt Julia's room one morning, and slipped butcher knives under the covers of her bed. "He just stood there and grinned," she said. Serial killer Carl Panzram himself wrote: "All of my family are as the average human beings are. They are honest and hard working people. All except myself. I have been a human-animile ever since I was born. When I was very young at 5 or 6 years of age I was a thief and a lier and a mean despisable one at that. The older I got the meaner I got." German child killer Peter Kurten had drowned two playmates by the tender age of nine.

Are these children just born bad? Environment alone cannot explain deranged behavior too many abused and neglected children grow up to be law-abiding citizens. If there is a genetic explanation, its a slippery, discreet mutation. We don't see entire families of serial killers. There is no such thing as a "kill gene", but research is revealing some genetic tendencies to violent behavior. In other words, bad seeds blossom in bad environments.

One study of twins who were raised apart, done by Yoon-Mi Hur and Thomas Bouchard in 1997, revealed a strong link between impulsivity and sensation-seeking behavior, "attributed almost entirely to genetic factors." Both sensation-seeking traits and impulsivity have been "found to be higher in drug abusers, delinquents, and psychopaths."

Do Serial Killers Have an Extra Chromosome?

Multiple murderer Bobby Joe Long had an extra X (female) chromosome, otherwise known as Klinefelter's syndrome, which meant he had the female hormone estrogen circulating in higher amounts in his system. His breasts grew during puberty, which caused him great embarrassment. Long, however, has an abundance of other serial killer prerequisites. He suffered traumatic and repeated head injuries, among other things.

Richard Speck
Richard Speck

Conversely, an extra Y (male) chromosome was once in vogue as an explanation to violence. Mass murderer Richard Speck's legal defense said he had an XYY genetic makeup, but further tests proved this wrong. While an extra male chromosome seems like a logical explanation for mutant-aggressive behavior, there is not much evidence that links the X or Y chromosome to serial killers.


High testosterone in itself is not a dangerous thing, but when it is combined with low levels of serotonin, the results might be deadly. Testosterone is associated with the need for dominance (many successful athletes and businessmen have high testosterone levels.) But since not everyone can be the top dog, serotonin keeps the tension from peaking, and mellows us out. When serotonin levels are abnormally low, however, frustration can lead to aggressive, even sadistic behavior, according to a study by Paul Bernhardt.

Heavy Metals

Some research has shown that violent offenders have higher trace levels of toxic heavy metals (manganese, lead, cadmium and copper) in their systems. Excess manganese lowers the level of serotonin and dopamine, which contributes to aggressive behavior. Alcohol increases the effects. James Huberty, the mass murderer, had excessive amounts of the toxic substance cadmium in his system.


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