People are fascinated by violent crime, and serial murder may be the most fascinating crime of all. Books, newspapers, television shows, and movies recount the destructive paths of those who kill repeatedly. Many of these accounts leave the impression that serial killers are distinct from other types of criminals and from the public at large. However, current knowledge on serial killers is based almost exclusively on a small number of case studies and a handful of moderately sized archival investigations. Thus, our current level of knowledge on serial murder is, at best, sketchy, and this knowledge may not stand up to more rigorous empirical testing. This entry reviews the definition of serial killing, demographics of serial murder, results of research on serial killers and their motivations, and typologies that have been used to classify serial killers.
Serial Killer Definition
Serial murder is defined by three key elements: number, time, and motivation. Most murderers have only one victim; serial killers, by definition, have multiple victims. The minimum number of victims listed in various definitions of serial murder proposed in recent years range from 2 to 10, with a modal value of 3. The time element in serial murder is designed to distinguish serial killers from mass murderers and spree killers. Whereas mass murderers have multiple victims in a single episode and spree killers have multiple victims in several separate but related episodes, in neither case is there an emotional cooling off period between murders. In contrast, in serial murder, there is a cooling off period of several days, weeks, months, or years. Finally, to differentiate serial killers from professional hit men, political terrorists, and military combatants, most definitions of serial murder omit individuals who kill exclusively for financial, political, or military gain.
Serial Killers Demographics
Men are responsible for the vast majority of crimes committed worldwide. An even greater percentage of men engage in serial murder. The ratio of male to female criminals, including those who commit single-incident homicides, is 9:1; the ratio of males to females who commit serial murder is somewhere in the neighborhood of 19:1. Although rare, female serial killers do exist and are more likely to work in pairs than male serial killers. In the United States, as many Blacks as Whites commit single-incident murder; the ratio of White to Black serial killers, on the other hand, is 5:1, which is roughly comparable with each group’s representation in the general population. Single-incident murders are normally committed by individuals in their early to mid-20s, while the initial murder in a series is normally committed by an individual in his or her late 20s to early 30s.
The victims of serial murder are just as likely to differ from the victims of single-incident homicide as the perpetrators of serial murder differ from the perpetrators of single-incident homicide. Young adults are the most common targets of serial murder, but victims could be anywhere from their early childhood to late adulthood. Some serial killers prefer male victims, others prefer female victims, and still others have no gender preference. According to recent estimates, females are more likely to be victimized by a serial killer than males, a pattern that runs counter to what has traditionally been observed in single-incident homicide, where male victims predominate. There are also single-serial differences in the victim-perpetrator relationship. Whereas the victims of single-incident murder are often family members, friends, and acquaintances, the victims of serial murder are nearly always strangers.
Research on Serial Murder
The research that has been conducted on serial murder has been largely descriptive in nature. Most serial killers work alone, although in 10% to 37% of cases serial killers work in pairs. When serial killers operate as a pair, one member ordinarily assumes the dominant role while the other member assumes the submissive role. Serial killers generally select their victims, and the victims they find most appealing are those that seem preoccupied, distracted, or vulnerable and those whose disappearance would be least likely to be noticed. Hence, single women, transients, runaway teenagers, and prostitutes are prime targets for serial murder. With respect to the method of murder, serial killers prefer to strangle, stab, or beat their victims rather than shoot them (the staple of single-incident murder). It has been speculated that “hands-on” murder techniques such as strangulation, stabbing, and beating offer the serial killer greater personal control over the victim than killing from a distance. Once the crime has been committed, the serial killer is more likely than the single-incident killer to try and deceive law enforcement by burying the body, moving the body to another location, or altering the crime scene.
There is no single psychological or personality profile that all serial killers fit, but there are certain characteristics that have been observed on a fairly regular basis in serial killers. First, serial killers are more likely to have a history of criminal involvement, often in the form of petty criminality, than a history of psychiatric treatment. Second, some serial killers exhibit tell-tale signs of a psychopathic personality. In several small-scale studies, approximately half the serial killers satisfied criteria for psychopathy as measured by Hare’s Psychopathy Checklist. This may explain why some serial killers are adept at disarming their victims without coercion and avoiding apprehension for an average of 4 to 5 years. Third, many serial killers have a rich fantasy life capable of fueling their appetite for murder, with or without the aid of additional facilitative conditions such as pornography and alcohol or drugs. Objects the serial killer collects from the crime scene or takes from the victim, commonly called trophies, not only help the killer relive the murder but can also trigger future killings. Several studies indicate that it is not unusual for an individual to entertain murder fantasies for several years before acting on them.
Motivation of Serial Killers
Research on the motivation behind serial homicide is complicated by the fact that motivation is often used to define serial murder and distinguish it from other categories of multiple murder (i.e., political terrorism, organized crime, military combat). It has traditionally been assumed that serial murder is driven by sexual motives, and in more than half of the serial killers interviewed, a clear sexual motive has been identified. Furthermore, in comparison with the emotional and social issues that frequently motivate single-incident homicide, serial homicide is more often motivated by sexual fantasies and desires. Having said this, the relationship between serial murder and sexual motivation may be an artifact of how serial murder is defined. Future researchers must consequently avoid confounding the criteria used to define serial murder (i.e., motivation) with the presumed motivation for serial murder by defining serial murder using variables other than sexual motivation.
Whether sexual motivation is an artifact of how serial murder is defined, nearly half of the serial killers who have been interviewed deny that there was a strong sexual component to their crimes. A small portion (4—5%) of serial murders appear to be motivated by psychosis, and slightly more are motivated by a strong profit motive. Revenge, on the other hand, may be a more powerful motive for serial murder than either psychosis or profit. There is preliminary evidence, for instance, that some serial killers target victims who display characteristics symbolic of a group or person they despise. Ted Bundy targeted young women with long dark hair parted down the middle because these were prominent features of a woman who had spurned him years earlier. John Wayne Gacy preyed on young males as a way, perhaps, of venting hatred toward his own homosexuality. An even stronger motive for serial murder is the power a person can derive from taking control of another person’s life. Forcing a stranger to submit to their every demand and then killing the person with their bare hands, a knife, or a piece of rope can be highly reinforcing to a serial killer.
Serial Killers Typologies
Several typologies have been advanced in an effort to classify serial killers into discrete categories. One of the more popular typologies, the organized/disorganized typology, was developed at the FBI’s Behavioral Science Unit in Quantico, Virginia. The organized serial killer is said to be of average to above-average intelligence, with good social skills, and a reasonably stable employment history. The murders enacted by an organized serial killer are usually well planned and typically involve the use of a weapon. Such individuals are said to leave an organized crime scene. A disorganized serial killer, on the other hand, possesses below average intelligence, weak impulse control, and poor social skills, leading to an unplanned attack that often results in a disorganized crime scene. The organized/disorganized typology was developed and validated on a group of 36 serial killers and other offenders who volunteered to be interviewed by the FBI. Recent empirical research has failed to support the organized/disorganized dichotomy, showing instead that most serial killers are organized and that they vary along a continuum of increased organization rather than splitting off into two groups.
Another popular typology of serial murder was proposed by Holmes and DeBurger. This typology consists of four categories: (1) visionary type; (2) mission-oriented type; (3) hedonistic type, which is broken down further into the lust killer, the thrill killer, and the creature-comfort killer; and (4) power/control type. Separate descriptions and motives are listed for each category in the typology. For instance, the visionary type is alleged to be motivated by delusions and hallucinations, is opportunistic in selecting victims, and leaves a messy crime scene, whereas the hedonistic type is motivated by personal enjoyment, pleasure, or gain, carefully selects victims based on predetermined criteria, and generally leaves a tidy crime scene. The problem with the Holmes and DeBurger typology is that because the four types are so poorly defined and the boundaries that separate them so indistinct, there is a high degree of overlap between types—a fatal flaw in any typology. Furthermore, there is no empirical support for the typology either as an effective shorthand in describing serial homicide or as a mechanism for predicting future behavior.
Future Research on Serial Killers
Serial murder is a rare event, thereby making it difficult to research. At present, nearly all of what we know about serial murder is based on a few case studies conducted on individuals who agreed to be interviewed by law enforcement and a handful of archival studies using information gleaned from newspapers, police files, and court documents. Consequently, there is a need for more empirical research on serial murder. First, a generally accepted definition of serial murder must be found so that it can serve as the standard for future research on serial homicide. The use of divergent definitions of serial murder and confounding definitions with variables (e.g., motivation) have thus far hindered progress in the field. Second, theoretical models, such as Hickey’s Trauma-Control Model, need to be created, tested, and refined. A good theory could reap tremendous benefits by advancing research and practice in the field. Third, alternatives to the traditional serial killer typologies need to be found. One such alternative is the instrumental-affective dimensional approach in which instrumental and affective motives for serial murder are allowed to coexist. Finally, more research needs to be devoted to prediction—not just as a way of narrowing down the field of suspects in a series of seemingly related murders but also as a way of understanding the factors that lead to serial murder and how some of these features can be ameliorated, altered, or changed.
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