The United States is reportedly home to an estimated 2,000 active serial killers, almost all of whom are men.In trying to understand the still-murky issue of why that is, some theories have pointed fingers at the primary male sex hormone testosterone as playing a role in their aggressive behavior.
In the same spirit, other studies consider sexual-homicide offenders over age 50 an aberration—murders committed by them account for only 0.5 percent of sexual homicides in the U.S.—which may be due to steep declines in their testosterone levels.
But are elevated levels of this important male sex hormone really such powerful catalysts for the making of a serial killer? And could a decline in testosterone put a halt to a killer’s murderous spree?
A&E True Crime spoke with John Mayer, Ph.D, an associate professor at the University of Nuevo Leon in Mexico and a clinical psychologist who specializes in violence, about the true relationship between testosterone and serial killers.
Do serial killers have higher levels of sex hormones than “normal” men?
If we look into the sex hormones or sexual urges of these killers, they are theoretically not any stronger than “normal” people, but because of incidents in their lives, they either get sexual pleasure in abnormal ways or kill to cover up sexual shame or guilt because of their urges.
There are no known studies that show conclusively that sexually motivated serial killers have higher testosterone levels. The key here is the behavioral or psychological need to cover-up or eliminate evidence of their abnormal sexual desires.
Are there any studies related to hormone levels in serial killers in general, even if their murders weren’t sexually motivated?
Testosterone is a hormone and the levels can fluctuate greatly in a person. Thus, the real test of such a theory would have to measure these levels at the time of the killing to have direct applicability to the serial killing or murder and, as you can guess, such conclusive research would be impossible to conduct.
Has any scientist ever done any research on serial killers’ testosterone levels later, while they are in prison?
No. These tests would only be done in the course of treating or diagnosing a particular medical problem for the inmate. It would be a violation of their civil rights in U.S. prisons to insist on such testing as a widespread, routine, mandated part of their incarceration.
So, if data exists, it would be part of the prisoner’s medical file and that is protected by the Health Insurance Portability and Accountability (HIPA) Act, just as every U.S. citizen’s medical records are.
Fantasies of rape or domination or even extremes in sexual expression are common in the sexual development of all men. But while most manage to outgrow that stage, serial killers don’t. Why is that the case??
What fails in the case of a [sexually motivated] serial killer is that in “normal” sexual development, these thoughts and urges get sublimated and shaped into conventional expressions because of the experience that a boy has with the potential sexual partners he encounters. In short, he learns that potential partners are disgusted or turned off by such desires, and is shaped into having sexual fantasies in a more conventional way.
This sublimation never happens in serial killers (for reasons not well known).
And what about serial killers who were married, like Dennis Rader (‘BTK’) or Herb Baumeister?
Serial killers are socially dysfunctional; as such, they are clueless about the normative social behaviors of others and the rules and boundaries of society. Some marry because in their primitive, dysfunctional way they are trying to copy social rules and norms. They are what I would call, acting, living ‘as if.’
Men who are 50 and older experience their own andropause, associated with a drop in the levels of testosterone. If you don’t see a connection between high levels of testosterone and serial killings, do you agree with theories saying sexual homicide offenders over 50 are rare?
Yes. I theorize that many sexually motivated serial killers decrease their activity as their sexual urges decrease physiologically. This operates much like it does in any human. Aging, nutrition, the environment and other conditions contribute to our lowered sexual drive.
And what follows then? Does the serial killer go on to lead a ‘normal’ life?
The interesting interplay here is that serial killers’ physical urges may decrease, but the excitement and stimulation they gain from the killing can continue on for some time. Thus, they may continue killing for the thrill of it until that gets boring to them or the energy that it takes to satisfy these urges is not worth the thrill they receive.