Søren Roest Korsgaard

The Zodiac Killer in View of Deindividuation Theory


The Zodiac killer began his official crime career at the end of December, 1968, when he gunned down David Arthur Faraday and Betty Lou Jensen just outside Vallejo, California. The double murder was quick and there was no evidence of intimate interaction between the killer and his victims. On July 4th, 1969, the Zodiac committed his third known murder when he sprayed Michael Mageau and Darlene Ferrin with bullets. Mageau lived to recant the horrific ordeal, and, from his statements as well as evidence collected, it is safe to opine that the attack was indeed swift, lacking of any intimate interaction, and no mask or uniform was documented to have been worn by the Zodiac. At the end of that July, the Zodiac began writing letters to the print media which went on for 5 years although a postcard was received in 1990 but cannot be conclusively linked to the Zodiac killer [1]. It is in these letters, as well as in other written pieces, that he christened himself as the “Zodiac.” In September 1969, he struck again and attacked another couple this time at Lake Berryessa, the largest lake in Napa County. The male victim fortunately survived. Investigators would later establish that the Zodiac had deviated from his established pattern and was in this incident dressed in a ceremonial/executioner’s costume while his eyes were hidden by sunglasses. To add onto that, he had a lengthy conversation with the couple, tied them up, and brutally stabbed both of them with a knife. This attack was significantly different, more intimate and physical than his previous murders. His last confirmed attack took place in October 1969, when he killed a taxi driver in San Francisco. The Zodiac continued sending letters and cards to the media, but he then stopped abruptly. When he returned in 1974, he no longer went by the name Zodiac but rather as “citizen” as was seen in his last communiqué which was in the form of a card. The card was different from his previous letters in almost all of its aspects, save for his handwriting. For the most part, his letters and cards had been filled with hate, anger, taunts, threats, and descriptions of some of his killings. The card from the citizen scolded the editor of the San Francisco Chronicle for indulging in “murder-glorification” by running the advertisement for the movie Badlands, which is loosely based on a killing spree by Charles Starkweather and his girlfriend that ended in 1958. Zodiac also made the point that “glorification of violence” was never justifiable. No solid theories have been proposed which explain (1) his use of a costume, and (2) his transition from a cold-blooded killer to a concerned citizen who is outraged by an advertisement for fictional violence. By means of deindividuation theory, the article argues that the physical and close interaction at Lake Berryessa was only possible for him due to the anonymity element of the superfluous garment and sunglasses, and that, due to a transition of mental and/or emotional forces as well as a transition related to self-awareness, he no longer regarded himself as a murderer. Herein, the Zodiac had become a citizen.

Deindividuation Theory

In the literature of social psychology, an emerging theory pertaining to anonymity and antisocial behavior began developing in the 1950s. Social psychologists wanted to understand the dynamics of aggression, especially in the context of groups. Studies have shown that under some circumstances individuals may lose their sense of being a distinct individual and this can lead to reduced self-evaluation due to a lack of self-awareness. In this scenario, anonymity reduces responsibility and transgressions of general social norms can more smoothly take place. It has been “long demonstrated that individuals who believe their identity is hidden are less inclined to act in an altruistic manner and are more inclined to engage in anti-social behavior [2].” The anonymity process may be facilitated or exacerbated by the introduction of certain cosmetic additions such as uniforms, masks, and body paint. The usage of military uniforms can result in an identification with a particular role (e.g. government mercenary), and the moral boundaries and restraints that generally characterized the individual gradually disappear. If such additions are worn at all times, much of their effect disappears; hence, many military forces have manufactured a variety of uniforms for special occasions such as combat. Deindividuation is especially associated with antisocial behavior committed by groups, e.g. during a riot, but also in individuals such as a rapist wearing a mask. The well-known Milgram experiment was replicated by Professor Phillip Zimbardo in 1969, but he changed the setup to test if deindividuation increased aggression. The subjects who were ordered to administer electric shocks were “either individuated with a name tag or deindividuated by wearing a hood. The deindividuated participants gave more shocks, supporting the idea of deindividuation [3].” In a 1973 cross-culture study it was discovered that warriors who wore face paint or garments to conceal their appearance were much more likely to kill, torture, and mutilate captives [4]. In a 1976 Halloween study it was discovered that among 1,300 trick-or-treating children who “were assigned to various conditions and given an opportunity to steal candy and money. Significantly more stealing was observed under conditions of anonymity and in the presence of a group [5].” In 1981, Malmuth and Check questioned male university students about, ”how likely they personally would be to rape if they could be assured of not being caught. On the average, about 35% indicated some likelihood of raping [6].” In a 2003 study of 500 violent attacks in Northern Ireland, 203 were carried out by attackers who had used a disguise. The author of the study concluded that “significant positive relationships existed between the use of disguises and several measures of aggression. Disguised offenders inflicted more serious physical injuries, attacked more people at the scene, engaged in more acts of vandalism, and were more likely to threaten victims after the attacks [7].” Several models have been set forth over the years to describe the variables that can lead to deindividuation; anonymity appears to be the essential factor.

The Costume

It is important to note that the use of the concealing elements went hand in hand with an amplified degree of violence and interaction with the victims, Bryan Hartnell and Cecilia Shepard, at Lake Berryessa on September 27, 1969 [8]. It is reasonable to say that the Zodiac felt less confident in his ability to mete out an intimate killing as his other confirmed murders and attacks were swift. The usage of the costume and sunglasses would have served as a barrier between him and the victims; his self-awareness and evaluation would have decreased allowing him to introduce a darker and elevated level of violence. Anonymity and deindividuation could have liberated the Zodiac, and he would have felt a loss of humane responsibility, allowing him to be free to act out his compulsions. When the Zodiac approached the victims, he told them an elaborate story about being an escaped convict who needed their car and money. He got both of the victims tied up and then savagely stabbed both of them repeatedly. Eventually, he did not take any items, and an investigation showed that he had concocted the story he fed to the victims. If Zodiac subconsciously needed to deindividuate himself, the spurious story and executioner’s type costume would have allowed him to identify with a particular role (probably as an executioner), very much like a soldier dressed in combat gear. The Zodiac would have been able to transform from a mere human being to a cold blooded killer on a mission, resulting in him becoming an objectified tool, hence lowering or blurring his sense of responsibility. In several of his ensuing letters, he quoted and alluded to the famous opera, the Mikado, and in particular he appeared to identify with the role of Ko-Ko, the Lord High Executioner whose function in the Opera is to “execute all those caught in the act of flirting [9].” On July 26, 1970, the Zodiac devoted nearly five pages of a letter to the opera as he described in lurid details how he would kill people in line with the work of the Lord High Executioner [10]. If the Zodiac assumed the role of an executioner, it would also have been a more feasible task for him to dehumanize his victims i.e. undermining their individuality.

The Citizen

In August of 1969, a letter arrived at the San Francisco Examiner. It began as follows, “This is the Zodiac speaking [11].” This was the first time that the killer had uniquely identified himself. In his initial three letters, he referred to himself as a “murderer” and a “killer [12].” The usage of the name “Zodiac” could have been a component of his deindividuation process as it would have allowed him to focus and identify with the skills, capabilities, and temperaments of his imagined character Zodiac, hence resulting in a loss of self-identity as well as an ability to block out possible feelings of guilt. When he resumed writing in 1974, he first sent an unsigned letter in January containing a reference to suicide [13]. In May, he sent the infamous card that was signed with “citizen [14].” Taken at face value, his allusion to suicide is significant inasmuch as suicide is related to high self-awareness [15]. As previously mentioned, deindividuation is especially characterized by anonymity and consequently reduced self-awareness; the individual becomes distant from the real self. It is therefore indicated that the Zodiac was going through a major transition from perceiving himself as a murderer to becoming a citizen who was outraged by violence. It should be mentioned that Zodiac’s individuation process or transition may have started as early as October 1969 as he committed his last confirmed murder in that month and ostensibly never killed again. Furthermore, professor of psychology, Dr. David van Nuys, has observed a dichotomy between the Zodiac’s initial letters from 1969 and those received in 1970, leading him to theorize that the Zodiac had lost control along this continuum. The Zodiac’s suicide reference, which was actually an inexact quotation from the Mikado, “might be a literal killing of his body, or it might signal the death of his ‘High Executioner’ sub-personality [16],” Dr. Nuys theorized. He suspected that “he may have been intitutionalized, or in therapy, or on some medication that was helping to bring his violent behavior under control [17].”


In view of the change in how the Zodiac killed swiftly using guns to the more intimate knife murder complete with a costume, it is quite possible that deindividuation came into play along with other psychological processes. The apparent loss of his Zodiac identity may have been the result of increased self-awareness; contrary, the citizen card could have been a form of manipulation or an attempt to get into the spotlight indirectly. The Zodiac’s letters often contained deception and manipulation [18]. It is even possible that the card could have been falsely attributed to him as handwriting analysis can produce conflicting results. A questioned document examiner working for the San Francisco Police Department concluded that Zodiac had penned it; however, an FBI expert noted handwriting variations, and he could not conclusively attribute it to the Zodiac’s hand, but it was “probably prepared [19]” by him.

About the writer: Søren Korsgaard, author of America’s Jack the Ripper: The Crimes and Psychology of the Zodiac Killer, is the editor of www.crimeandpower.com and webmaster of www.paulcraigroberts.org. Support Søren’s work by donating Bitcoin: 19Z22vsdaKJX4gy8GDy6J8QU1ZZ9EvSoEo   


1.  Korsgaard, Søren. “America’s Jack the Ripper: The crimes and psychology of the Zodiac Killer” (2017), p. 276.
2. Silke, A. ”Deindividuation, anonymity, and violence: Findings from Northern Ireland.” The Journal of Social Psychology.
3. ”Revise Psychology: Deindividuation” https://revisepsychology.wordpress.com/2012/05/15/ 2-deindividuation/
4. Watson, R. I. ”Investigation into deindividuation using a cross-cultural survey technique.” Journal of Personality and Social Psychology (1973).
5. Diener, E., Fraser, S. C., Beaman, A. L., & Kelem, R. T. ”Effects of deindividuation variables on stealing among Halloween trick-or-treaters.” Journal of Personality and Social Psychology (1976).
6. Malamuth, N. M. ”Rape proclivity among males.” Journal of Social Issues (1976). http://dx.doi.org/10.1111/j.1540-4560.1981.tb01075.x
7. Silke, A. ”Deindividuation, anonymity, and violence: Findings from Northern Ireland.” The Journal of Social Psychology.
8. Department of Justice, Bureao of Criminal Investigation and Investigation Report, Case Number 1-15-311-F9-5861, p. 19.
9. Douglas Oswell, THE ZODIAC AND THE UNABOMBER (Douglas Oswell 2007), p. 101.
10. Zodiac Letter. Received by the San Francisco Chronicle. Postmark: July 24, 1970.
11. Zodiac Letter. Received by the San Francisco Examiner. Postmark: August, 1969.
12. Zodiac Letter. Received by the San Francisco Chronicle. Postmark: July 31, 1969.
13. Ibid, January 29, 1974.
14. Ibid, May 8, 1974.
15. Selimbegovic, L., Chatard, A. ”The mirror effect: Self-awareness alone increases suicide thought accessibility.” Consciousness and Cognition (2013).
16. Kelleher, Van Nuys, ”This is the Zodiac Speaking: Into the Mind of a Serial Killer” (Praeger Publishers 2002), p. 186.
17. Ibid.
18. Korsgaard, Søren. “America’s Jack the Ripper: The crimes and psychology of the Zodiac Killer” (2017), p. 117-118.
19. Freedom of Information and Privacy Acts, Subject: Zodiac Killer, File Number: 9-HQ-49911, Section 4 Federal Bureau of Investigation, p. 181.

Author Since: Apr 09, 2019

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