To Catch a Killer: Analyzing Serial Killers

DataRes at UCLA
9 min readJul 21, 2023

Authors: Megha Velakacharla (Project Lead), Bryan Kwan, Impana Chimmalagi, Jasmine Jungreis, Jodie Chen

Serial killers have long captivated the public imagination, inspiring shows and movies like “Mindhunter” and “You”. These real-life monsters puzzle us, challenging our fundamental understanding of humanity and raising questions about how their minds work. This article will delve deep into the world of serial killers, attempting to shed light on their motives, and unraveling the complex web of their crimes. A dataset with hundreds of history’s most notorious serial killers, as well as data from the FBI’s Supplementary Homicide Report, will be examined, and the background of murderers and victims will also be explored to distinguish patterns that may indicate serial killer activity.

The mean number of victims of serial killers fluctuates a lot throughout the years, with peaks appearing around the early 1970s, 1980s, and 1990s. Many serial killers arise from turbulent childhoods when there was chaos in the household. Abuse and disorder in the family, when combined with other factors, such as genetic predispositions, can evoke the behaviors and characteristics of serial killers. During WWII (1938–1945), there were a lot of these types of households, as people were already exposed to the violence of the war outside of their households. This can explain such rises during the late 1900s from the generation of people that were raised during wartime.

The visualization above compares the number of proven victims of serial killers to the number of possible victims over time. Again, the number of victims spiked between the 1970s and 1990s, and the ratio of possible to proven victims also spiked during this time. Authorities were not able to prove as many serial killings during this period. One reason for this spike, apart from the societal impacts of WWII, could be the availability of forensic technology, which has steadily improved since those times. Specifically, forensic DNA evidence only began being admissible in criminal cases in 1986. Additionally, the large computerized databases that allow for the identification and tracking of patterns in killings were not yet readily available at that time.

Evidently, the United States has had the most amount of serial killers throughout history. The accessibility and availability of guns is likely the main reason for this discrepancy. Firearms have the advantage of speed and efficiency that can allow killers to more easily maintain anonymity and be harder to catch. Additionally, the development of the interstate highway system in the U.S. not long before this time period increased the mobility of many killers, giving them an advantage when it came to finding victims and evading the authorities. Also during this era, lead was permitted to be in gasoline, and many studies have linked higher blood lead levels in kids to many developmental impediments and behavioral issues, which in extreme cases can develop into serial killer tendencies.

Examining Gender Differences

In the 1900s, there were 45 male serial killers on record compared to 27 female serial killers. The number of male serial killers increased until its peak of 922 in the 1990s, more than 20 times as many as in 1900. This compared to the 69 female serial killers recorded in the 1990s produces a 13:1 ratio of male to female serial killers. However, the discrepancy between male and female serial killers extends far beyond their sizable ratio. There are also notable differences in the strategies employed by killers and the victims targeted by male and female serial killers.

Discrepancies in the Processes of Male and Female Serial Killers

Male

Female

Primary Method

Gunshot

Poison

Primary Treatment

Rape

Quick

Primary Motive

Sexual

Financial

Stalk Victim

65.4%

3.6%

Family Victim

42.3%

1.7%

There is a disparity in motives between male and female killers, as there is a sexual component to the majority of murders performed by male serial killers. 68% of male serial killers raped their victims, while 88% of female serial killers opted for a quick murder with no additional treatment. This suggests that the murders enacted by male serial killers are often sexually motivated. In contrast, the primary motive of female serial killers is financial gain.

This could explain why only 3.6% of female serial killers stalk their victims prior to the murder compared to 65.4% of male serial killers. Evolutionary psychologists have proposed the early gender roles of hunting and gathering as another possible explanation for this discrepancy. Male serial killers tend to “hunt” their victims through stalking succeeded by torture and overkill. While the leading method of murder in the case of male serial killers is by gunshot, female serial killers more frequently opt for poison or suffocation.

The overall relationship between the sexes of serial killers and victims also provides some important insights. For female serial killers, there is a higher proportion of their victims being male than female. This makes sense as female killers are known to kill men for revenge or financial/material gain. They also tend to target men that have close relations with them, particularly romantic connections, for the money. Interestingly, there is a higher proportion of female perpetrators killing females than male perpetrators killing females. And more male perpetrators with male victims than female victims. This contrasts popular belief that male perpetrators tend to target females for sexual lust, which raises the question of what motives male serial killers have for killing men. Could it also be sexual lust or something else? Perhaps this shift from male serial killers targeting females to targeting males has evolved over the years.

Analyzing Demographics

Los Angeles homicide reports data visualized above illustrates that in general, perpetrators tend to target victims of their own race, except for Native Americans who tend to target white people. This could mean many killers have motivations related to race or perhaps, the prejudice that exists within their area means they have a better chance of luring a victim that is of their own race. For example, white serial killers would “stand out” if they targeted black people or prowled around black neighborhoods. Black people may not be as willing to trust someone who’s white or of another race that approaches them. They may be more likely to trust a black person, making black serial killers likely to target them. This may explain why Samuel Little, who was black, tended to kill black people — he had a higher chance of gaining the trust of his black victims. This might also suggest that serial killers tend to prowl around ethnically diverse areas where there’s not as much racial prejudice such as big cities or hunt in areas where their major demographic is their own race so that they can keep a low profile.

Analyzing Age

Serial killers tend to be between 19 and 30 years old. A person is less likely to be a serial killer if they are older than 40. Most serial killers, regardless of the age group, target people 30 and under. This makes sense as serial killers are known to target younger, vulnerable people. Thus, their victims are not as likely to be reported missing by their families, making it easy for serial killers to escape unscathed. Along with the race analysis, this further illustrates that serial killers do not kill impulsively; they are often extremely strategic and calculating, consciously selecting victims and hunting in areas that allow them to keep a low profile so that they can continue their killing spree.

Classifying Serial Killer Activity from Homicides

The relationship categories of stranger and unknown combined have the highest percentages of incidents of 6.1% and 71.7% respectively. This can be attributed to the fact that perpetrators who have a direct relationship with their victims are easier to track down as opposed to strangers/unknown victims who have no ties to them. Serial killers who aim to perform sprees and target as many victims as they can are more likely to exhibit behavior resulting in a lower risk of being caught, and choosing unrelated victims would accomplish this behavior most out of all the other connected relationships. Generalizing this to homicides, the acquaintance relationship is also quite common (with the second-highest percentage of 8.1%). For homicides (single-kills) compared to killing sprees, they don’t share the objective of being able to commit more than a singular murder, meaning it might be less difficult for homicide perpetrators to target those adjacent to themselves.

In order to obtain a holistic understanding of the homicide data, observe that there are certain data points in which victim counts are nonzero and perpetrator counts are zero; this can be related to accidental homicide. For the opposite case (nonzero perpetrator count and victim count of zero), these incidents can be related to attempted homicide. Now, moving on to the bulk of the visualization: there seems to be a higher concentration of lower victim count numbers for higher perpetrator count numbers. On the other hand, as the data reaches lower numbers for perpetrator counts, the concentration of lower victim counts widens out into higher victim count numbers, but in less concentration, possibly signaling serial killer activity. The data points on the far left strengthen this observation, with a perpetrator count of 1 but victim counts of 9 and 10. In general, as perpetrator counts reach lower numbers, victim count numbers seem to increase, a property similar to serial killer activity where single perpetrators have large numbers of corresponding victims.

From the graph above, it is evident that there are two abnormally high spikes in March 1990 and April 1995, with victim counts of 918 and 1686 respectively. For these two months, the victim count is significantly higher than the perpetrator count (the differences between the victim and perpetrator counts during these two months respectively are 639 and 1046). Thus, these two periods of time may be attributed to mass killing activities. In April 1995, domestic terrorist Timothy James McVeigh perpetrated the Oklahoma City Bombing that killed 168 people and injured more than 680 people. McVeigh is an instance of how drastic spikes in victim count, along with less drastic perpetrator count spikes can be attributed to increased killing activities, of which serial killing is a subset. Overall, disparities in perpetrator and victim counts can be related to serial killer activities, who are more common to have unknown or stranger relationships with their victims.

Conclusion

Studying serial killers provides important insights into their patterns and motivations. The U.S. leads in the number of serial killers, and factors such as turbulent childhoods, forensic technology, and societal influences contribute to fluctuations in serial killer activity. Gender differences show that male killers are often sexually motivated, while females seek financial gain. Strange spikes in victim counts and discrepancies between victim and perpetrator counts within homicides can be linked to mass killing incidents and potentially serial killer activity. Overall, analyzing serial killer data sheds light on the dark side of human behavior and the complex factors involved in these crimes.

Works Cited

https://www.kaggle.com/datasets/vesuvius13/serial-killers-dataset

https://www.southflalaw.com/history-evolution-and-case-studies-of-dna-evidence.html#:~:text=DNA%20evidence%20has%20been%20legally,innocence%20or%20guilt%20since%201986.

https://archives.fbi.gov/archives/news/stories/2009/april/highwayserial_040609

https://www.brookings.edu/blog/up-front/2017/06/01/new-evidence-that-lead-exposure-increases-crime/

https://www.brookings.edu/blog/up-front/2017/06/01/new-evidence-that-lead-exposure-increases-crime/

https://www.britannica.com/biography/Timothy-McVeigh

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