Drawing of brain

You do not have be enlightened to realize that there is something different about serial killers. Clearly, the horror stories from victims and police reports will soon have you believing that something has to be very different about these people for them to do what they do, and whatever that something is has to be encoded in the brain somewhere, somehow. I would like to talk through some of the psychological disorders that could be behind the possibility for serial killing, but firstly, I would like to clarify what I mean by ‘encoded in the brain.’ I simply mean that at any one moment in time our brains have developed in one particular way and that way controls the statistical likelihood of certain behaviors occurring under certain circumstances, in this case, serial killing.

Serial killer itself is not a diagnosis, but the term serial murder has been defined by the F.B.I. as “the unlawful killing of two or more victims by the same offender(s) in separate events.” This definition, as far as law enforcement is concerned, is very useful, as these behavioral traits are unique to the type of person who is likely to offend again if not apprehended. But what psychological diagnoses could account for this kind of behavior? This question is made even more important by the fact that forming an experimental group consisting solely of serial killers would be extremely difficult to establish.

The most broadly recognized mental disorder associated with serial killing is Antisocial Personality Disorder (APD). This is a cluster B personality in the DSM IV and is intimately related with psychopathy. Psychopathy is not a clinical diagnosis, but it is considered a developmental disorder by neuroscientists (Blair, 2006). Many individuals with APD are not psychopathic, but a number of them, especially the ones who exhibit traits such as limited empathy and grandiosity, do demonstrate psychopathy (Hare & Babiek, 2007). Psychopathic traits such as charm, manipulation, and intimidation have been recognized by the F.B.I. as being thoroughly connected to serial murder (see here for more details), although it’s important to realize that not all psychopaths are serial killers.

A cool academic point to note about psychopathy is that we know the kinds of behaviors psychopaths reliably exhibit (such as superficial charm and a lack of empathy; for an inclusive list see Hare, 1990), we know that they typically have a low resting heart rate (Lorber, 2004), and we also know that that they are likely to have significant differences in their brain, such as reduced prefrontal gray matter (Raine et al., 2000), amygdalar abnormalities (Blair, 2003), and asymmetric hippocampi (Raine et al., 2004). One can only speculate how these brain differences could be implicated in psychopathic behavior, but it does mean that if we scanned the brain of a serial killer and measured their heart rate, these are the kind of differences we could expect to find.

Could there be any other mental condition implicated in serial killing, other than psychopathy or APD? We can only speculate, but a good place to look would be at the other cluster B personality disorders. Borderline Personality Disorder (BPD) is characterized by emotional instability, anxiety, and psychotic-like symptoms where those afflicted can suddenly become very paranoid or suspicious of others (Skodol et al., 2002). BPD has also been included by Simon Baron-Cohen as a disorder that results in zero degrees of empathy, a term he uses to describe conditions where the afflicted does not seem to have any empathy for others (Baron-Cohen, 2011). BPD is often comorbid with impulsive aggression, too (Skodol et al., 2002).

So how could BPD result in serial killing? We can only speculate, but suddenly becoming very paranoid or suspicious of others, having no empathy for anyone, and perhaps being subject to impulsive aggression, means that should an individual with BPD display with all of these traits at once, there could be an assault that results in the loss of life. If there is a situational or environmental trigger for these outbursts, the killing could become serial.  This would be in contrast to psychopathic serial killers, where the killing is usually pre-meditated.

The brains of those with BPD are less understood. Impulsive aggression is characteristic of most cluster B disorders, and this seems to be related to low levels of serotonin (Skodol et al., 2002); this has resulted in attempts to treat BPD with SSRIs. Scientists have found altered levels of metabolism in the anterior cingulate cortex (De la Fuente et al., 1997) and reduced matter in the prefrontal cortex (Lyoo et al., 1998) in those with BPD.

There do not seem to be any neurological studies that have found anything special about Narcissistic Personality Disorder (NPD), another cluster B disorder. But NPD is mentioned by Baron-Cohen as another disorder where the afflicted have no empathy for others. This automatically suggests prefrontal and limbic abnormalities, perhaps similar to APD and BPD, but unlike BPD, those afflicted with NPD do not suffer temporary psychotic-like symptoms. It must also be acknowledged, here, that psychopaths are very narcissistic, and so deciding on a diagnosis between APD and NPD is a very difficult task.

The last disorder I would like to mention as a candidate is schizophrenia. Schizophrenics, especially when experiencing psychotic symptoms (such as auditory and visual hallucinations), can become violent. Accounts of schizophrenia and serial murder are mixed. Castle & Hensley (2002) claim that there has never been a validated case of a schizophrenic serial killer, but Ronald Markman M.D., who served as a forensic psychiatrist, details the life of Richard Chase, who was also known as The Vampire of Sacramento (Markman & Bosco, 1989). Chase was diagnosed numerous times as a paranoid schizophrenic, before he committed a number of murders towards the end of the 1980s.

A common characteristic of schizophrenics, however, is to have jumbled and confused thoughts, which when considered in light of cold, calculated, and premeditated murders, it is harder to merit schizophrenia as a driving force behind serial murder. If our serial killer was a schizophrenic, however, we could expect to see enlarged lateral ventricles (brain tissue surrounding the ventricles has diminished), depleted myelin sheaths in the cerebral cortex, and abnormal clusters of neurons (Bear, Connors, & Paradiso, 2007).

There are other implicated disorders in violent behavior and it must be understood that it is not uncommon to have more than one of them. Schizoid and Schizotypy personality disorders are known to share similarities with schizophrenia, but again, on their own the probability of them being implicated in serial murder is low to nonexistent. 

Copyright Jack Pemment, 2013 


Baron-Cohen, S. (2011) The science of evil, Basic Book, New York

Bear, M.F.; Connors, B.W.; Paradiso, M.A. (2007) Neuroscience – Exploring the brain (3rd Ed.), Lippincott, Williams & Wilkins, Baltimore

Blair, R.J.R. (2003) Neurobiological basis of psychopathy, British Journal of Psychiatry, 182, 5-7

Blair, R.J.R. (2006) The emergence of psychopathy: Implications for the neuropsychological approach to developmental disorders, Cognition, 101, 414-442

Castle, T.; Hensley, C. (2002) Serial killers with military experience: Applying learning theory to serial murder, International Journal of Offender Therapy and Comparative Criminology, 46(4), 453-465

De La Fuente, J.M.; Goldman, S.; Stanus, E.; Vizuete, C.; Morlan, I.; Bobes, J.; Mendlewicz, J. ( 1997) Brain glucose metabolism in borderline personality disorder, Journal of Psychiatric Research, 31(5), 531-541

Hare, R.D.; Harpur, T.J.; Hakistan, A.R.; Forth, A.E.; Hart, S.D.; Newman, J.P. (1990) The revised psychopathy checklist: Reliability and factor structure, Psychological Assessment, 2(3), 338-341

Hare, R.D.; Babiek, P. (2007) Snakes in Suits: When psychopaths go to work, Harper Collins, New York

Lorber, M.F. (2002) Psychophysiology of aggression, psychopathy, and conduct problems: A meta-analysis, Psychological Bulletin, 130(4), 531-552

Lyoo, I.K.; Han, M.H.; Cho, D.Y. (1998) A brain MRI study in subjects with borderline personality disorder, Journal of Affective Disorders, 50, 235-243

Markman, R.; Bosco, D. (1989) Alone with the Devil: Famous cases of a courtroom psychiatrist, Double Day, New York

Raine, A.; Lencz, T.; Birhle, S.; LaCasse, L.; Colletti, P. (2000) Reduced prefrontal gray matter volume and reduced autonomic activity in antisocial personality disorder, Arch Gen Psychiatry, 57, 119-127

Raine, A.; Ishikawa, S.S.; Arce, E.; Lencz, T.; Knuth, K.H.; Birhle, S.; LaCasse, L.; Colletti, P. (2004) Hippocampal structural asymmetry in unsuccessful psychopaths, Biological Psychiatry, 55, 185-191

Skodol, A.E.; Siever, L.J.; Livesley, W.J.; Gunderson, J.G.; Pfohl, B.; Widiger, T.A. (2002) The borderline diagnosis II: Biology, genetics, and clinical course, Biological Psychiatry, 51, 951-96

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