What is a Serial Killer?

Serial Killers: Unraveling the Mind and Methods Behind the Madness

Serial killers, both chilling and compelling, have long captured the public’s imagination, not as much for its horror but for the psychological and investigative puzzles it presents. While overly sensationalized by media and popular culture, the truth behind serial killers is far more complex than the tropes suggest. It is a complex phenomenon influenced by psychological, social, and situational factors that go well beyond the myths of lone madmen, genius sociopathy and ritualistic killings.

What Defines Serial Killer?

At its core, serial killer refers to the unlawful killing of two or more victims by the same offender(s), in separate events, usually over a period of time. The FBI’s definition includes a cooling-off period between murders, distinguishing it from mass or spree killings. This period serves as a psychological reset for the killer, making each act a distinct and planned event rather than part of a single emotional outburst or continuous rampage.

History

Serial killers have occurred throughout history since ancient times. One of the earliest documented cases involved Locusta, a Roman woman hired by Agrippina the Younger, mother of Nero, to poison several members of the imperial family. Locusta was executed in 69 ce. Serial killers also were documented in medieval Europe, such as England, Germany, Hungary, and Italy. Liu Pengli, Prince of Jidong, was the grandson of Emperor Wen. In 2nd century BC, he murdered over a hundred people in total, seizing their possessions, as recorded by Sima Qian in Records of the Great Historian.

The known incidence of serial killers increased dramatically in the early 19th century, particularly in Europe, though this development has been attributed to advances in law-enforcement techniques and increased news coverage rather than to an actual rise in the number of occurrences. Serial killers of the early 19th century included a German woman who poisoned more than a dozen people; the Irish-born William Burke and William Hare, who killed at least 15 people in Scotland in the 1820s; and an Austrian woman who reportedly fed children to her family. The most famous case of serial killer in the 19th century was that of Jack the Ripper, who killed at least five women in London in 1888. Shortly afterward the United States recorded the comparably dramatic case of Herman Webster Mudgett (“H.H. Holmes”), who confessed to 27 murders and was executed in Philadelphia in 1896.

Newspaper clip. 1888. Jack The Ripper headline

20th Century

In the 20th century, cases of serial killings received widespread coverage in the news media. The serial killing phenomenon in the United States was especially prominent from 1970 to 2000, which has been described as the “golden age of serial murder”. Murderers became known by sensationalized nicknames, such as the Boston Strangler, the Düsseldorf Vampire (Peter Kürten), the Monster of Florence, and the Killer Clown (John Wayne Gacy) or BTK (Dennis L. Rader). Their crimes, which both horrified and fascinated the public, raised numerous social and legal issues, such as the tendency of police to be less thorough in murder investigations when the victims were poor or of low social status.

From left to right: Jeffrey Dahmer, Son of Sam, Ted Bundy

The Misconceptions and Media Mythology

Popular media has painted serial killers as evil geniuses or deeply disturbed loners driven by elaborate rituals. The reality is more mundane and more frightening, as many serial killers lead seemingly normal lives as neighbors, family, colleagues. They may be married, hold steady jobs, and blend into their communities. This “mask of sanity” enables them to evade detection for extended periods.

Contrary to popular belief, most do not possess above-average intelligence. In fact, many score in the normal or even below-average IQ range.

Moreover, while fictional portrayals often emphasize a single, deviant motive, such as lust or revenge, serial killers can be driven by a combination of motivations that evolve over time. These can include power, control, financial gain, or even a twisted sense of mission or ideology. The narrative of the lone, white, male killer is also increasingly being challenged, as cases involving women and individuals from diverse racial and socioeconomic backgrounds gain attention.

Motives and Typologies

Motives of serial killers can include anger, thrill-seeking, attention seeking, and financial gain

• The most common motivation seems to be the enjoyment of killing (35.0%) followed by financial gain, (30.0%), and then anger (16.9%)
• Psychosis as a primary motive is rare (.5%).
• Approximately 10% of serial killers did not have the same motive for killing each victim.

Serial Killers Motives – U.S. Only

Efforts to categorize serial killers have led to the development of typologies, the most well-known being the Holmes and DeBurger classification: visionary, mission-oriented, hedonistic, and power/control.

• Visionary killers suffer from psychotic breaks with reality, often believing they are compelled by voices or visions. For example, Herbert Mullin believed he had to kill to prevent earthquakes in California.
• Mission-oriented killers believe they are eliminating undesirable elements from society. Joseph Paul Franklin, who targeted individuals based on race and religion, is an example.
• Hedonistic killers derive pleasure from the act itself, whether it be lust, thrill, or comfort (as in financial gain). Ted Bundy and Jeffrey Dahmer are infamous for deriving personal gratification from their killings.
• Power/control killers are driven by a desire to dominate and exert ultimate control over their victims. Dennis Rader, known as BTK (Bind, Torture, Kill), exemplifies this type.

However, these categories often overlap, and real-life offenders rarely fit neatly into a single box. Motives may shift with time, and different phases of a killer’s life may see different behavioral patterns.

The Role of Childhood and Environment

While no single factor can predict serial killings, many offenders report a history of childhood trauma, neglect, or abuse. This early exposure to violence can desensitize individuals to suffering and may lay the groundwork for later aggression. Some researchers point to the Macdonald triad bedwetting, arson, and cruelty to animals as potential early warning signs, though this theory is highly contested. On average, 50% of serial killers suggest that they have experienced psychological abuse, 36% have experienced physical abuse, and 26% have experienced sexual abuse (Mitchell & Aamodt, 2005)

Edmund Kemper, who murdered ten people including his own grandparents and mother, experienced severe emotional abuse and was institutionalized as a youth.

Environmental stressors, such as poverty, unstable family life, and lack of social support, may also contribute. Still, not all individuals who experience these conditions become violent, highlighting the complexity of predicting such behavior.

The incidence of child abuse in serial killers
H. Mitchell and M. G. Aamodt
Journal of Police and Criminal Psychology, 20(1):40–47, 2005
DOI: 10.1007/BF02806705
ISBN: 1936-6469

Fifty serial killers who murdered for the primary goal of attaining sexual gratification, termed lust killers, were studied to determine the prevalence of childhood abuse. Information regarding the childhood abuse sustained by each killer was obtained primarily from biographical books, newspaper articles, and online sites. Abuse was categorized into physical abuse, sexual abuse, psychological abuse, and neglect and was then compared to societal norms from 2001. Abuse of all types excluding neglect was significantly higher in the serial killer population. For serial killers, the prevalence of physical abuse was 36%; sexual abuse was 26%; and psychological abuse was 50%. Neglect was equally prevalent in the serial killer (18%) and societal norm populations.

Victimology and Target Selection

Serial killers often select victims based on availability, vulnerability, and desirability. Marginalized groups, such as the unhoused, sex workers or individuals with substance use disorders, are disproportionately targeted. Their disappearances may go unnoticed longer and be less vigorously investigated.

Gary Ridgway, the Green River Killer, targeted sex workers and runaways, murdering at least 49 women.

Contrary to the notion of ritualistic consistency, many serial killers show variation in their victim selection and killing methods. They may adjust their tactics to avoid detection or simply evolve in their methods and preferences over time. This inconsistency can make linking crimes more difficult.

• On average, serial killers who exclusively kill female victims are about three years older
  than those who exclusively kill male victims.
• On average, serial killers who only killed White victims are about four years older than those who only killed Black victims.

Serial Killer Victimology

Investigative Challenges

Despite advances in forensic science and criminal profiling, catching a serial killer remains a formidable task. The cooling-off period, the randomness of victim selection, and lack of prior connection to the victims all complicate investigations. Jurisdictional fragmentation further hinders progress when crimes occur in different areas with little coordination between law enforcement agencies.

Criminal profiling, while valuable, is not a panacea. It offers insights based on patterns observed in previous cases but cannot predict individual behavior with certainty. Geographic profiling, victimology, and behavioral analysis can help narrow down suspect pools, but these are tools, not guarantees.

Gathering evidence

• The disposal of human remains can cause delays in locating the victim’s body. This leads to evidence being collected and discovered in an unpredictable order, which can complicate the identification of patterns
• Pattern emergence. In the absence of physical evidence, links between crimes may go unnoticed until a pattern persists long enough to exceed mere coincidence
• Opportunistic/arbitrary target selection. The arbitrary selection of specific victims within the targeted group introduces unpredictability, affecting the chances of establishing a direct link between the offender and each victim.
• Vulnerable victims. The fact that a quarter of all victims of serial killers are sex trade workers suggests that offenders may knowingly exploit the vulnerability and social and spatial isolation of these individuals, presenting an opportunity for easy access to them
• The unidentified victim. When the disappearance of a person goes unreported, as a homicide victim they may remain unidentified. In the case of the Green River Killer, 10% of the victims remained unidentified even after the investigation concluded.

Identifying a suspect

• Evidence decay. The delayed discovery of a homicide victim diminishes the chances of acquiring forensic evidence necessary for the identification, apprehension, and conviction of the perpetrator
• Case linkage and jurisdictional challenges. Case linkage involves connecting crimes based on offender behaviour, but offenders may change tactics and cross jurisdictional lines to hunt for victims

Proving guilt

• Time. Homicide investigations require immediate action within the critical first 48 h, as emphasized by law enforcement training
• Cost. Costs are another significant aspect to consider in serial homicide investigations, especially those involving sexual elements and strangers, which attract media attention and intensify pressure on investigators due to heightened public expectations and scrutiny

Source: Rossouw, Z., & Palys, T. (2024). “Baggage in the business”: The investigative challenges of serial homicide. The Police Journal, 98(1), 249-268. https://doi.org/10.1177/0032258X241269482 (Original work published 2025)

The Role of Technology

Technological innovations have played a pivotal role in recent breakthroughs. DNA analysis, database integration (such as CODIS), and digital forensics have all contributed to solving cold cases. The arrest of the Golden State Killer, decades after his last known crime, is a testament to the power of modern forensic methods, particularly genetic genealogy.

Social media and internet activity also provide digital footprints that can aid investigators. However, technology is a double-edged sword as it also allows offenders to find and lure victims more easily and anonymously.

Female Serial Killers: Breaking the Mold

Although male offenders dominate the known cases, female serial killers are not unheard of. Their crimes are often less violent and more subtle, involving poisoning or smothering rather than overt physical aggression. Motivations tend to revolve around financial gain, caretaking gone awry, or revenge. Their victims are often those within their domestic or professional circles, such as children, older patients, or spouses.

Aileen Wuornos, who killed seven men in Florida, claimed she acted in self-defense against sexual assault. Her case challenged stereotypes of female killers and drew intense media scrutiny.

Aileen Wuornos

The underrepresentation of women in serial killing statistics may reflect both genuine differences and systemic biases in detection and classification. Women’s methods often leave fewer forensic clues and may be mistaken for natural deaths, delaying or preventing criminal investigations.

International Perspectives

Serial killers are not specific to the United States, though much of the research and media coverage has focused there. Cases from countries like Russia, South Africa, and Mexico reveal different cultural, social, and legal contexts in which serial killing unfolds. In some regions, political instability or lack of law enforcement resources allows killers to operate unchecked for longer periods.

Andrei Chikatilo, the “Butcher of Rostov” murdered over 50 people in the Soviet Union. His crimes went unsolved for years due to investigative missteps and political denial about the existence of such crimes in a communist state.

Yet, the psychological drivers, such as a need for control, suppressed rage, or deviant pleasure, transcend borders. Global efforts to understand and combat serial killings are increasingly collaborative, with agencies sharing data and investigative techniques across countries.

Why Are We Fascinated?

Peoples enduring fascination with serial killers comes from a mix of fear, curiosity and a desire for understanding. These crimes force us to confront the darkest aspects of human nature and question the limits of empathy, morality, and justice.

One of the main reasons for the interest in serial killers is protection. Women to avoid being in a situation where they become a victim, and men to be able to protect.

True crime media, documentaries, and fiction have amplified this interest, sometimes distorting facts but also generating greater awareness. Educational initiatives and responsible journalism can leverage this interest to promote accurate information and foster informed discussions about violence, psychology, and criminal justice.

Serial killer fascination in television and media

Moving Forward: Prevention and Awareness

Prevention efforts must focus on early intervention and support for at-risk individuals, particularly children exposed to violence or trauma. Better mental health services, stronger community ties, and improved communication between agencies can all help in identifying potential threats before they escalate.

While serial killers remain rare, their impact on victims’ families and communities is profound and lasting. Understanding the phenomenon in its full complexity is essential not only for solving crimes but for preventing them.

In shedding the myths and embracing the nuances, society can begin to grapple with serial killers not as a source of entertainment, but as a crime requiring science and vigilance in solving it.

Video Playlist

Sources:

A Behaviour Sequence Analysis of Serial Killers’ Lives: From Childhood Abuse to Methods of Murder

Britannica

The social study of serial killers

The incidence of child abuse in serial killers

FBI

Rossouw, Z., & Palys, T. (2024). “Baggage in the business”: The investigative challenges of serial homicide. The Police Journal, 98(1), 249-268. https://doi.org/10.1177/0032258X241269482 (Original work published 2025)