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A serial killer is traditionally defined as a person who has killed three or more people over a period of more than a month, with down time (a "cooling off period") between the murders, and whose motivation for killing is usually based on psychological gratification. Some sources, such as the FBI, disregard the "three or more" criteria and define the term as "a series of two or more murders, committed as separate events, usually, but not always, by one offender acting alone" or, including the vital characteristics, a minimum of two murders. Often, a sexual element is involved in the killings, but the FBI states that motives for serial murder include "anger, thrill, financial gain, and attention seeking". The murders may have been attempted or completed in a similar fashion and the victims may have had something in common; for example, occupation, race, appearance, sex, or age group.
Serial killers are not the same as mass murderers, nor are they spree killers, who commit murders in two or more locations with virtually no break in between; however, cases of extended bouts of sequential killings over periods of weeks or months with no apparent "cooling off" period or "return to normalcy" have caused some serial killer experts to suggest a hybrid category of "spree-serial killer".
The English term and concept of "serial killer" is commonly attributed to former FBI Special agent Robert Ressler in the 1970s. Author Ann Rule postulates in her 2004 book Kiss Me, Kill Me that the English-language credit for coining the term "serial killer" goes to LAPD detective Pierce Brooks, creator of the ViCAP system. In his book Serial Killers: The Method and Madness of Monsters, criminal justice historian Peter Vronsky argues that while Ressler might have coined the term "serial homicide" within law enforcement when guest lecturing in 1974 at Bramshill Police Academy in Britain, the terms "serial murder" and "serial murderer" appear in 1966 in John Brophy's book The Meaning of Murder. Moreover, Vronsky reports that the term "serial killer" does not appear in Anne Rule's seminal book on Ted Bundy, The Stranger Beside Me, published in 1980, when the term was not yet in popular use.
Some commonly found characteristics of serial killers include:
- Generally having an average or low-average IQ, although they are often described, and perceived, as possessing IQs in the above-average range. A sample of 174 IQs of serial killers had a median IQ of 93; only serial killers who used bombs had an average IQ above the population mean.
- Often, they have trouble staying employed and tend to work in menial jobs. The FBI, however, states, "Serial murderers often seem normal; have families and/or a steady job." Other sources state they often come from unstable families.
- They were often abused—emotionally, physically and/or sexually—by a family member.
- Fetishism, partialism and necrophilia are paraphilias which involve a strong tendency to experience the object of erotic interest almost as if it were a physical representation of the symbolized body. Individuals engage in paraphilias which are organized along a continuum; participating in varying levels of fantasy perhaps by focusing on body parts (partialism), symbolic objects which serve as physical extensions of the body (fetishism), or the anatomical physicality of the human body; specifically regarding its inner parts and sexual organs (one example being necrophilia).
- A disproportionate number exhibit one, two, or all three of the Macdonald triad (see below) of predictors of psychopathy:
- Many are fascinated with fire setting.
- They are involved in sadistic activity; especially in children who have not reached sexual maturity, this activity may take the form of torturing animals.
- More than 60 percent, or simply a large proportion, wet their beds beyond the age of 12. However, recent authorities (see citations in the Enuresis section of the Macdonald triad article) question or deny the statistical significance of this figure; subsequent research suggests that bedwetting may not be related to psychopathy.
- They were frequently bullied or socially isolated as children or adolescents. Henry Lee Lucas was ridiculed as a child and later cited the mass rejection by his peers as a cause for his hatred of everyone. Kenneth Bianchi was teased as a child because he urinated in his pants and suffered twitching, and as a teenager was ignored by his peers.
- Some were involved in petty crimes, such as theft, fraud, vandalism, dishonesty or similar offenses.
There are exceptions to these criteria, however. For example, Harold Shipman was a successful professional (a General Practitioner working for the NHS). He was considered a pillar of the local community, even winning a professional award for a children's Asthma clinic and was interviewed by Granada Television's World in Action. Dennis Nilsen was an ex-soldier turned civil servant and trade unionist who had no previous criminal record when arrested. Neither were known to have exhibited many of these signs. Vlado Taneski was a career journalist who was caught after a series of articles he wrote gave clues that he had murdered people; Taneski was a crime reporter. Russell Williams was a successful and respected career Royal Canadian Air Force Officer who was convicted of the murder of two women, along with fetish burglaries and rapes.
Some serial killers additionally exhibit various degrees of psychopathy, though this is not always the case. Psychopaths lack empathy and guilt, are egocentric and impulsive, and theoretically do not conform to social, moral and legal norms. Instead, psychopaths often follow a distinct set of rules which they have created for themselves. They may appear to be normal and often quite charming, a state of adaptation that psychiatrist Hervey Cleckley called the "mask of sanity". In the DSM-IV, psychopathy is listed under Axis II Personality disorders NOS. It is a disorder mainly defined by traits of both antisocial personality disorder and narcissism. In the near future, the concept of psychopathy requires revision because the new version of the DSM (DSM-V) no longer includes narcissism. Forensic specialists and researchers most commonly use the Hare Psychopathy Checklist (PCL-R; developed by Robert D. Hare) to assess psychopathy and differentiate it from antisocial personality disorder (ASPD). The PCL-R is an expert-rated checklist that scores people on interpersonal/affective traits (Factor 1) and behavioral/impulsive traits (Factor 2). The studies have shown that while 50–80 percent of criminals were diagnosed with ASPD, only 15–30 percent scored as primary psychopaths on the PCL-R test.
Serial killers exhibiting degrees of ASPD, however, are often aware of how to hide many of the characteristics listed above in order to blend with the rest of society. Serial killer Ed Kemper became particularly notorious for doing this when he tricked psychiatrists into believing he was "cured" seven years after being admitted to the Atascadero State Hospital for the murders of his two grandparents. Three years after his release, Kemper went on to murder at least eight additional victims.
Many serial killers have faced similar problems in their childhood development. Hickey's Trauma Control Model explains how early childhood trauma can set the child up for deviant behavior in adulthood; the child's environment (either their parents or society) is the dominant factor in whether or not the child's behavior escalates into homicidal activity.
Family, or lack thereof, is the most prominent part of a child's development because it is what the child can identify with on a regular basis. "The serial killer is no different than any other individual who is instigated to seek approval from parents, sexual partners, or others." This need for approval is what influences children to attempt to develop social relationships with their family and peers, but if they are rejected or neglected, they are unable to do so. This results in the lowering of their self-esteem and helps develop their fantasy world in which they are in control. According to the Hickey's Trauma Control Model the development of a serial killer is based on an early trauma followed by facilitators (this can be porn, drugs, alcohol, or any number of things as what constitutes as a facilitator is dependent on individual circumstances) and disposition (an inability to attach being one common factor).
Family interaction also plays an important role in a child's growth and development. "The quality of their attachments to parents and other members of the family is critical to how these children relate to and value other members of society." Wilson and Seaman (1990) conducted a study on incarcerated serial killers and what they felt was the most influential factor that contributed to their homicidal activity. Almost all of the serial killers in the study had experienced some sort of environmental problems during their childhood, such as a broken home caused by divorce, or a lack of discipline in the home. It was common for the serial killers to come from a family that had experienced divorce, separation, or the lack of a parent. Furthermore, nearly half of the serial killers had experienced some type of physical and sexual abuse and even more had experienced emotional neglect. When a parent has a drug or alcohol problem, the attention in the household is on the parents rather than the child. This neglect of the child leads to the lowering of their self-esteem and helps develop a fantasy world in which they are in control. Hickey's Trauma Control Model supports how the neglect from parents can facilitate deviant behavior especially if the child sees substance abuse in action. This then leads to disposition (the inability to attach), which can further lead to homicidal behavior unless the child finds a way to develop substantial relationships and fight the label they receive. If a child receives no support from those around him or her, then he or she is unlikely to recover from the traumatic event in a positive way. As stated by E. E. Maccoby, "the family has continued to be seen as a major—perhaps the major—arena for socialization".
Children who do not have the power to control the mistreatment they suffer sometimes create a new reality to which they can escape. This new reality becomes their fantasy that they have total control of and becomes part of their daily existence. In this fantasy world, their emotional development is guided and maintained. According to Garrison (1996), "the child becomes sociopathic because the normal development of the concepts of right and wrong and empathy towards others is retarded because of the child's emotional and social development occurs within his self-centered fantasies. A person can do no wrong in his own world and the pain of others is of no consequence when the purpose of the fantasy world is to satisfy the needs of one person" (Garrison, 1996). Boundaries between fantasy and reality are lost and fantasies turn to dominance, control, sexual conquest, and violence, eventually leading to murder. Fantasy can lead to the first step in the process of a dissociative state, which, in the words of Stephen Giannangelo, "allows the serial killer to leave the stream of consciousness for what is, to him, a better place".
Criminologist Jose Sanchez reports, "the young criminal you see today is more detached from his victim, more ready to hurt or kill ... The lack of empathy for their victims among young criminals is just one symptom of a problem that afflicts the whole society." Lorenzo Carcaterra, author of Gangster (2001), explains how potential criminals are labeled by society, which can then lead to their offspring also developing in the same way through the cycle of violence. The ability for serial killers to appreciate the mental life of others is severely compromised, presumably leading to their dehumanization of others. This process may be considered as an expression of the intersubjectivity associated with a cognitive deficit regarding the capability to make sharp distinctions between other people and inanimate objects. For these individuals, objects can appear to possess animistic or humanistic power while people are perceived as objects. Before he was executed, serial killer Ted Bundy stated media violence and pornography had stimulated and increased his need to commit homicide, although this statement was made during last-ditch efforts to appeal his death sentence. However, correlation is not causation (a disturbed physiological disposition, psychosis, lack of socialization, or aggressiveness may contribute to both fantasy creation and serial killing without fantasy creation generally contributing to serial killing for instance). There are exceptions to the typical fantasy patterns of serial killers, as in the case of Dennis Rader, who was a family man and the leader of his church.
Organized, disorganized, and mixed 
The FBI's Crime Classification Manual places serial killers into three categories: organized, disorganized, and mixed (i.e., offenders who exhibit organized and disorganized characteristics). Some killers descend from being organized into disorganized behavior as their killings continue.
Organized nonsocial offenders usually have above average intelligence, with a mean IQ of 113. They often plan their crimes quite methodically, usually abducting victims, killing them in one place and disposing of them in another. They often lure the victims with ploys appealing to their sense of sympathy. For example, Ted Bundy would put his arm in a fake plaster cast and ask women to help him carry something to his car, where he would beat them unconscious with a tire iron, and carry them away. Others specifically target prostitutes, who are likely to go voluntarily with a stranger. They maintain a high degree of control over the crime scene, and usually have a solid knowledge of forensic science that enables them to cover their tracks, such as burying the body or weighing it down and sinking it in a river. They follow their crimes in the news media carefully and often take pride in their actions, as if it were all a grand project. The organized killer is usually socially adequate, has friends and lovers, and sometimes even a spouse and children. They are the type who, when/if captured, are most likely to be described by acquaintances as kind and unlikely to hurt anyone. Bundy and John Wayne Gacy are examples of organized serial killers.
Disorganized serial killers, on the other hand, often have average to below average intelligence, with a mean IQ of 92.5. They are usually far more impulsive, often committing their murders with a random weapon available at the time, and usually not attempting to hide the body. They are likely to be unemployed, a loner, or both, with very few friends. They often turn out to have a history of mental illness, and their modus operandi (M.O.) or lack thereof is often marked by excessive violence and sometimes necrophilia and/or sexual violence.
Medical professionals 
Some people with a pathological interest in the power of life and death tend to be attracted to medical professions or acquiring such a job. These kinds of killers are sometimes referred to as "angels of death" or angels of mercy. Medical professionals will kill their patients for money, for a sense of sadistic pleasure, for a belief that they are "easing" the patient's pain, or simply "because they can". One such killer was nurse Jane Toppan, who admitted during her murder trial that she was sexually aroused by death. She would administer a drug mixture to patients she chose as her victims, lie in bed with them and hold them close to her body as they died.
Female serial killers 
Female serial killers are rare compared to their male counterparts, while all serial killers are relatively rare. The FBI states that serial murder is "estimated to comprise less than one percent of all murders committed in any given year". Other sources state that female serial killers historically represent nearly one in every six known serial murderers in the United States between 1800 and 2004 (64 females from a total of 416 known offenders): over 15% of all known American serial killers have been women, with a collective number of victims between 427-612. Eric W. Hickey states that although popular perception sees "Black Widow" female serial killers as something of the Victorian past, in his statistical study of female serial killer cases reported in the USA since 1826, approximately 75% occurred since 1950.
Some studies have concluded that female serial killers tend to murder men for material gain, are usually emotionally close to their victims, and generally need to have a relationship with the victim, hence the traditional cultural image of the "Black Widow". Some recent studies, however, indicate that since 1975, increasingly strangers are marginally the most preferred victim of female serial killers, and only 26% of female serial killers kill for material gain only. Victims are not confined to males/husbands, as one "analysis of 86 female serial killers from the U.S. found that the victims tended to be spouses, children or the elderly". In the U.S., 51% of all female serial killers murdered at least one woman and 31% percent murdered at least one child. The methods they use for murder are frequently covert or low-profile, such as murder by poison (the preferred choice for killing). They commit killings in specific places, such as their home or a health-care facility, or at different locations within the same city or state. Other methods used by female serial killers include shootings (used by 20%), suffocation (16%), stabbing (11%), and drowning (5%). Although female serial killers are often reported as murdering for money or other material gain, others frequently do it for attention, as an addiction, or as a result of psychopathological behavioral factors. While some female serial killers have been diagnosed with Münchausen syndrome, "little research has been conducted focusing on the societal influences—particularly gender roles and expectations of women—which contribute to these women committing multiple murders". Each killer will have her own proclivities, needs and triggers, as specific reasons can only be obtained from the killer herself. "In a review of published literature on female serial murder, sexual or sadistic motives are believed to be extremely rare in female serial murderers, and psychopathic traits and histories of childhood abuse have been consistently reported in these women." A new study by Eric W. Hickey (2010) of 64 female serial killers in the United States indicated that sex was one of several motives in 10% of the cases, enjoyment in 11% and control in 14%. In some cases, women have been involved as an accomplice with a male serial killer as a part of a serial killing "team".
Kelleher and Kelleher (1998) created several categories to describe female serial killers. They used the classifications of black widow, angel of death, sexual predator, revenge, profit or crime, team killer, question of sanity, unexplained and unsolved. In using these categories, they observed that most women fell into the categories of black widow and team killer. In describing murderer Stacey Castor, forensic psychiatrist Dr. James Knoll offered a psychological perspective on what defines a "black widow" type. In simple terms, he described it as a woman who kills two or more husbands or lovers for material gain. Though Castor was not officially defined as a serial killer, it is likely that she would have killed again. Peter Vronsky (2007) maintains that female serial killers today often kill for the same reason males do: as a means of expressing rage and control. He suggests that sometimes the theft of the victims’ property by the female "Black Widow" type serial killer appears to be for "material gain" but really is akin to a male serial killer’s collecting of totems (souvenirs) from the victim as a way of exerting continued control over the victim and reliving it.
A notable exception to the typical characteristics of female serial killers is Aileen Wuornos, who killed outdoors instead of at home, used a gun instead of poison, killed strangers instead of friends or family, and killed for personal gratification. The most prolific female serial killer in all of history is allegedly Elizabeth Báthory. Countess Elizabeth Báthory de Ecsed (Báthory Erzsébet in Hungarian, August 17, 1560 – August 21, 1614) was a countess from the renowned Báthory family. After her husband's death, she and four collaborators were accused of torturing and killing hundreds of girls and young women, with one witness attributing to them over 600 victims, though the number for which they were convicted was 80. Elizabeth herself was neither tried nor convicted. In 1610, however, she was imprisoned in the Csejte Castle, where she remained bricked in a set of rooms until her death four years later.
An article which addressed some of the misperceptions of female criminality has appeared in the forensic literature. The Perri and Lichtenwald article addresses the current research regarding female psychopathy and includes case studies of female psychopathic killers featuring Münchausen syndrome by proxy, cesarean section homicide, fraud detection Homicide, female kill teams, and a female serial killer.
Ethnicity and serial killer demographics in the U.S. 
The racial demographics regarding serial killers are often subject to debate. In the United States, the majority of reported and investigated serial killers are white males, from a lower-to-middle-class background, usually in their late twenties to early thirties. However, there are African American, Asian, and Hispanic (of any race) serial killers as well, and, according to the FBI, based on percentages of the U.S. population, whites are not more likely than other races to be serial killers. Criminal profiler Pat Brown says serial killers are usually reported as white because the media typically focuses on "All-American" white and pretty female victims who were the targets of white male offenders, that crimes among minority offenders in urban communities, where crime rates are higher, are under-investigated, and that minority serial killers likely exist at the same ratios as white serial killers for the population. She believes that the myth that serial killers are always white might have become "truth" in some research fields due to the over-reporting of white serial killers in the media.
Some authors state that African American serial killers are as prevalent, or more so, in proportion to the African American population. According to some sources, the percentage of serial killers who are African American is estimated to be between 13 and 22 percent. Another study has shown that 16 percent of serial killers are African American, what author Maurice Godwin describes as a "sizeable portion". Anthony Walsh writes, "While it is true that most serial killers are white males, white (Anglo) males are actually slightly underrepresented in the serial killer ranks in terms of their proportion of the general male population" and that "[w]hatever the true proportion of black serial killers in the United States is or has been, it is greater than the proportion of African Americans in the general population." Popular racial stereotypes about the lower intelligence of African-Americans, and the stereotype that serial killers are white males with "bodies stacked up in the basement and strewn all over the countryside" may explain the media focus on serial killers that are white and the failure to adequately report on those that are black.
The motives of serial killers are generally placed into four categories: visionary, mission-oriented, hedonistic and power or control; however, the motives of any given killer may display considerable overlap among these categories.
Visionary serial killers suffer from psychotic breaks with reality, sometimes believing they are another person or are compelled to murder by entities such as the Devil or God. The two most common subgroups are "demon mandated" and "God mandated".
Herbert Mullin believed the American casualties in the Vietnam War were preventing California from experiencing the Big One. As the war wound down, Mullin claimed his father instructed him via telepathy to raise the number of "human sacrifices to nature" in order to delay a catastrophic earthquake that would plunge California into the ocean. David Berkowitz ("Son of Sam") is also an example of a visionary killer. He claimed a demon transmitted orders through his neighbor's dog and instructed him to commit murder.
Mission-oriented killers typically justify their acts as "ridding the world" of a certain type of person perceived as undesirable, such as homosexuals, prostitutes, or people of different ethnicity or religion; however, they are generally not psychotic. For example, the Zebra killers in the San Francisco Bay Area specifically targeted Caucasians. Some see themselves as attempting to change society, often to cure a societal ill.
This type of serial killer seeks thrills and derives pleasure from killing, seeing people as expendable means to this goal. Forensic psychologists have identified three subtypes of the hedonistic killer: "lust", "thrill" and "comfort".
Sex is the primary motive of lust killers, whether or not the victims are dead, and fantasy plays a large role in their killings. Their sexual gratification depends on the amount of torture and mutilation they perform on their victims. The serial sexual murderer has a psychological need to have absolute control, dominance, and power over his victims, and the infliction of torture, pain, and ultimately death is used in an attempt to fulfill his need.  They usually use weapons that require close contact with the victims, such as knives or hands. As lust killers continue with their murders, the time between killings decreases or the required level of stimulation increases, sometimes both.
Kenneth Bianchi, one of the "Hillside Stranglers", murdered women and girls of different ages, races and appearance because his sexual urges required different types of stimulation and increasing intensity. Jeffrey Dahmer searched for his perfect fantasy lover—beautiful, submissive and eternal. As his desire increased, he experimented with drugs, alcohol, and exotic sex. His increasing need for stimulation was demonstrated by the dismemberment of victims, whose heads and genitals he preserved, and by his attempts to create a "living zombie" under his control (by pouring acid into a hole drilled into the victim's skull). Dahmer once said, "Lust played a big part of it. Control and lust. Once it happened the first time, it just seemed like it had control of my life from there on in. The killing was just a means to an end. That was the least satisfactory part. I didn't enjoy doing that. That's why I tried to create living zombies with … acid and the drill." He further elaborated on this, also saying, "I wanted to see if it was possible to make—again, it sounds really gross—uh, zombies, people that would not have a will of their own, but would follow my instructions without resistance. So after that, I started using the drilling technique." He experimented with cannibalism to "ensure his victims would always be a part of him".
The primary motive of a thrill killer is to induce pain or terror in their victims, which provides stimulation and excitement for the killer. They seek the adrenaline rush provided by hunting and killing victims. Thrill killers murder only for the kill; usually the attack is not prolonged, and there is no sexual aspect. Usually the victims are strangers, although the killer may have followed them for a period of time. Thrill killers can abstain from killing for long periods of time and become more successful at killing as they refine their murder methods. Many attempt to commit the perfect crime and believe they will not be caught. Robert Hansen took his victims to a secluded area, where he would let them loose and then hunt and kill them. In one of his letters to San Francisco Bay Area newspapers, the Zodiac Killer wrote "[killing] gives me the most thrilling experience it is even better than getting your rocks off with a girl". Coral Watts was described by a surviving victim as "excited and hyper and clappin' and just making noises like he was excited, that this was gonna be fun" during the 1982 attack. Slashing, stabbing, hanging, drowning, asphyxiating, and strangling were among the ways Watts killed.
Comfort (profit) 
Material gain and a comfortable lifestyle are the primary motives of comfort killers. Usually, the victims are family members and close acquaintances. After a murder, a comfort killer will usually wait for a period of time before killing again to allow any suspicions by family or authorities to subside. They often use poison, most notably arsenic, to kill their victims. Female serial killers are often comfort killers, although not all comfort killers are female. Dorothea Puente killed her tenants for their Social Security checks and buried them in the backyard of her home. H. H. Holmes killed for insurance and business profits. Professional killers ("hitmen") may also be considered comfort serial killers. Richard Kuklinski charged tens of thousands of dollars for a "hit", earning enough money to support his family in a middle-class lifestyle (Bruno, 1993).
Some, like Puente and Holmes, may be involved in and/or have previous convictions for theft, fraud, non payment of debts, embezzlement and other crimes of a similar nature. Dorothea Puente was finally arrested on a parole violation, having been on parole for a previous fraud conviction.
The main objective for this type of serial killer is to gain and exert power over their victim. Such killers are sometimes abused as children, leaving them with feelings of powerlessness and inadequacy as adults. Many power- or control-motivated killers sexually abuse their victims, but they differ from hedonistic killers in that rape is not motivated by lust but as simply another form of dominating the victim. Ted Bundy traveled around the United States seeking women to control.
Many serial killers claim that a violent culture influenced them to commit murders. Ted Bundy stated that hardcore pornography was responsible for his actions. Others idolise figures for their deeds or perceived vigilante justice, such as Peter Kürten, who idolised Jack the Ripper, or John Wayne Gacy and Ed Kemper, who both idolised John Wayne.
Biological and sociological 
||The examples and perspective in this section deal primarily with the United States and do not represent a worldwide view of the subject. (May 2010)|
Theories for why certain people commit serial murder have been advanced. Some theorists believe the reasons are biological, suggesting serial killers are born, not made, and that their violent behavior is a result of abnormal brain activity. Holmes and Holmes believe that "until a reliable sample can be obtained and tested, there is no scientific statement that can be made concerning the exact role of biology as a determining factor of a serial killer personality." The "Fractured Identity Syndrome" (FIS) is a merging of Charles Cooley's "looking glass self" and Erving Goffman's "virtual" and "actual social identity" theories. The FIS suggests a social event, or series of events, during one's childhood or adolescence results in a fracturing of the personality of the serial killer. The term "fracture" is defined as a small breakage of the personality which is often not visible to the outside world and is only felt by the killer.
"Social Process Theory" has also been suggested as an explanation for serial murder. Social process theory states that offenders may turn to crime due to peer pressure, family, and friends. Criminal behavior is a process of interaction with social institutions, in which everyone has the potential for criminal behavior. A lack of family structure and identity could also be a cause leading to serial murder traits. A child used as a scapegoat will be deprived of their capacity to feel guilt. Displaced anger could result in animal torture, as identified in the Macdonald triad, and a further lack of basic identity.
The "military theory" has been proposed as an explanation for why serial murderers kill, as some serial murderers have served in the military or related fields. According to Castle and Hensley, 7% of the serial killers studied had military experience. This figure may be a proportional under-representation when compared to the number of military veterans in a nation's total population. For example, according to the United States census for the year 2000, military veterans comprised 12.7% of the U.S. population; in England, it was estimated in 2007 that military veterans comprised 9.1% of the population. Though by contrast, about 2.5% of the population of Canada in 2006 consisted of military veterans.
There are two theories that can be used to study the correlation between serial killing and military training: Applied learning theory states that serial killing can be learned. The military is training for higher kill rates from servicemen while training the soldiers to be desensitized to taking a human life. Social learning theory can be used when soldiers get praised and accommodated for killing. They learn, or believe that they learn, that it is acceptable to kill because they were praised for it in the military. Serial killers want accreditation for the work that they have done.
In both military and serial killing, the offender or the soldier may become desensitized to killing as well as compartmentalized; the soldiers do not see enemy personnel as "human" and neither do serial killers see their victims as humans. The theories do not imply that military institutions make a deliberate effort to produce serial killers; to the contrary, all military personnel are trained to recognize when, where, and against whom it is appropriate to use deadly force, which starts with the basic Law of Land Warfare, taught during the initial training phase, and may include more stringent policies for military personnel in law enforcement or security. They are also taught ethics in basic training. A number may have been conscripts, such as Arthur Shawcross.
Notable cases 
Among modern serial killers who have some background or experience in the military are some notable examples. David Russell Williams was a colonel in the Royal Canadian Air Force who escalated from panty heists to serial rape to serial murder. Robert Lee Yates killed prostitutes in Washington state while he was in the U.S. Army. Serial killer Randy Steven Kraft killed U.S. Marines after he was discharged for mental health reasons; he reasoned: "If I couldn't be a Marine, they can't either". Jeffrey Dahmer served in the U.S. Army as a Combat medic until he was medically discharged. John Reginald Christie served in the British Army during World War I, and later served in the London Metropolitan Police during World War II. Dennis Nilsen was a cook with the British Army, and later served in the Metropolitan Police and the civil service. Few of these individuals experienced combat situations during their military careers; some exhibited mental or behavioral problems separate from or prior to their military experiences.
FBI: Issues and practices 
In 2008, the Federal Bureau of Investigation (FBI) published a handbook entitled Serial Murder which was the product of a symposium held in 2005 to bring together the many issues surrounding serial murder, including its investigation.
According to the FBI identifying one, or multiple, murders as being the work of a serial killer is the first challenge an investigation faces. Especially if the victim(s) come from a marginalized or high risk population and is normally linked through forensic or behavioral evidence (FBI 2008). Should the cases cross multiple jurisdictions, the law enforcement system in the United States is fragmented and thus not configured to detect multiple similar murders across a large geographic area (Egger 1998). The FBI suggests utilizing databases and increasing interdepartmental communication. Keppel (1989) suggests holding multi-jurisdictional conferences regularly to compare cases giving departments a greater chance to detect linked cases and overcome linkage blindness. One such collaboration, the Radford/FGCU Serial Killer Database Project was proposed at the 2012 FDIAI Annual Conference. Utilizing Radford's Serial Killer Database as a starting point, the new collaboration, hosted by FGCU Justice Studies, has invited and is working in conjunction with other Universities to maintain and expand the scope of the database to also include spree and mass murders. Utilizing over 150 data points, multiple-murderer methodology and victimology; researchers and Law Enforcement Agencies can build case studies and statistical profiles to further research the Who, What, Why and How of these types of crimes.
Leadership, or administration, should play a small or virtually non-existent role in the actual investigation past assigning knowledgeable or experienced homicide investigators to lead positions. The administration's role is not to run the investigation but to establish and reaffirm the primary goal of catching the serial killer, as well as provide support for the investigators. The FBI (2008) suggests completing Memorandums of Understanding to facilitate support and commitment of resources from different jurisdictions to an investigation. Egger (1998) takes this one step further and suggests completing mutual aid pacts, which are written agreements to provide support to each other in a time of need, with surrounding jurisdictions. Doing this in advance would save time and resources that could be used on the investigation.
Organization of the structure of an investigation is key to its success, as demonstrated by the investigation of the Green River Killer. Once a serial murder case was established a task force was created to track down and arrest the offender. Over the course of the investigation, for various reasons, the task force's organization was radically changed and reorganized multiple times - at one point including more than 50 full-time personnel, and at another, only a single investigator. Eventually, what lead to the end of the investigation was a conference of 25 detectives organized to share ideas to solve the case (Guillen 2007).
The FBI handbook provides a description of how a task force should be organized but offers no additional options on how to structure the investigation. While it appears advantageous to have a full-time staff assigned to a serial murder investigation it can become prohibitively expensive. For example, the Green River Task Force cost upwards of two million dollars a year (Guillen 2007), and as was witnessed with the Green River Killer investigation, other strategies can prevail where a task force fails.
A common strategy, already employed by many departments for other reasons, is the conference (Egger 1990) in which departments get together and focus on a specific set of topics. With serial murders, the focus is typically on unsolved cases, with evidence thought to be related to the case at hand.
Similar to a conference is an information clearing house in which a jurisdiction with a suspected serial murder case collects all of its evidence and actively seeks data which may be related from other jurisdictions (Egger 1990). By collecting all of the related information into one place they provide a central point in which it can be organized and easily accessed by other jurisdictions working toward the goal of arresting an offender and ending the murders.
Already mentioned was the task force (Egger 1990, FBI 2008, Keppel 1989) which provides for a flexible, organized, framework for jurisdictions depending on the needs of the investigation. Unfortunately due to the need to commit resources (manpower, money, equipment, etc.) for long periods of time it can be an unsustainable option.
In the case of the investigation of Aileen Wournos the Marion County Sheriff coordinated multiple agencies without any written or formal agreement (Egger 1998). While not a specific strategy for a serial murder investigation this is certainly a best practice in so far as the agencies were able to work easily together toward a common goal.
Finally once a serial murder investigation has been identified, utilization of an FBI Rapid Response Team can assist both experienced and inexperienced jurisdictions in setting up a task force. This is completed by organizing and delegating jobs, by compiling and analyzing clues, and by establishing communication between the parties involved (Egger 1998).
Resource augmentation 
During the course of a serial murder investigation it may become necessary to call in additional resources; the FBI defines this as Resource Augmentation. Within the structure of a task force the addition of a resource should be thought of as either long term, or short term. If the task force's framework is expanded to include the new resource, then it should be permanent and not removed. For short term needs, such as setting up road blocks or canvassing a neighborhood, additional resources should be called in on a short term basis. The decision of whether resources are needed short or long term should be left to the lead investigator and facilitated by the administration (FBI 2008). The confusion and counter productiveness created by changing the structure of a task force mid investigation is illustrated by the way the Green River Task Force's staffing and structure was changed multiple times throughout the investigation. This made an already complicated situation more difficult, resulting in the delay or loss of information, which allowed Ridgeway to continue killing (Guillen 2007). The FBI model does not take into account that permanently expanding a task force, or investigative structure, may not be possible due to cost or personnel availability. Egger (1998) offers several alternative strategies including; using investigative consultants, or experienced staff to augment an investigative team. Not all departments have investigators experienced in serial murder and by temporarily bringing in consultants, they can educate a department to a level of competence then step out. This would reduce the initially established framework of the investigation team and save the department the cost of retaining the consultants until the conclusion of the investigation.
The FBI handbook (2008) and Keppel (1989) both stress communication as paramount. The difference is that the FBI handbook (2008) concentrates primarily on communication within a task force while Keppel (1989) makes getting information out to, and allowing information to be passed back from patrol officers a priority. The FBI handbook (2008) suggest having daily e-mail or in person briefings for all staff involved in the investigation and providing periodic summary briefings to patrol officer and managers. Looking back on a majority of serial murderer arrests, most are exercised by patrol officers in the course of their every day duties and unrelated to the ongoing serial murder investigation (Egger 1998, Keppel 1989). Keppel (1989) provides examples of Larry Eyler, who was arrested during a traffic stop for a parking violation, and Ted Bundy, who was arrested during a traffic stop for operating a stolen vehicle. In each case it was uniformed officers, not directly involved in the investigation, who knew what to look for and took the direct action that stopped the killer. By providing up to date (as opposed to periodic) briefings and information to officers on the street the chances of catching a serial killer, or finding solid leads, are increased.
Data management 
A serial murder investigation generates staggering amounts of data, all of which needs to be reviewed and analyzed. A standardized method of documenting and distributing information must be established and investigators must be allowed time to complete reports while investigating leads and at the end of a shift (FBI 2008). When the mechanism for data management is insufficient, leads are not only lost or buried but the investigation can be hindered and new information can become difficult to obtain or become corrupted. During the Green River Killer investigation, reporters would often find and interview possible victims or witnesses ahead of investigators. The understaffed investigation was unable to keep up the information flow, which prevented them from promptly responding to leads. To make matters worse, investigators believed that the journalists, untrained in interviewing victims or witnesses of crimes, would corrupt the information and result in unreliable leads (Guillen 2007).
In history 
Historical criminologists have suggested that there may have been serial murders throughout history, but specific cases were not adequately recorded. Some sources suggest that legends such as werewolves and vampires were inspired by medieval serial killers. In Africa, there have been periodic outbreaks of murder by Lion and Leopard men. In Tanganyika, the Lion men committed an estimated 200 murders in a single three-month period.
Liu Pengli of China, cousin of the Han Emperor Jing, was made Prince of Jidong in the sixth year of the middle period of Jing's reign (144 BC). According to the Chinese historian Sima Qian, he would "go out on marauding expeditions with 20 or 30 slaves or young men who were in hiding from the law, murdering people and seizing their belongings for sheer sport". Although many of his subjects knew about these murders, it was not until the 29th year of his reign that the son of one of his victims finally sent a report to the Emperor. Eventually, it was discovered that he had murdered at least 100 people. The officials of the court requested that Liu Pengli be executed; however, the emperor could not bear to have his own cousin killed, so Liu Pengli was made a commoner and banished.
In the 15th century, one of the wealthiest men in Europe and a former companion-in-arms of Joan of Arc, Gilles de Rais, sexually assaulted and killed peasant children, mainly boys, whom he had abducted from the surrounding villages and taken to his castle. It is estimated that his victims numbered between 140 and 800. The Hungarian aristocrat Elizabeth Báthory allegedly tortured and killed as many as 650 girls and young women before her arrest in 1610.
Thug Behram, a gang leader of the Indian Thuggee cult of assassins, has frequently been said to be the world's most prolific serial killer. According to numerous sources, he was believed to have murdered 931 victims by means of strangulation with a ceremonial cloth between 1790 and 1830. According to some estimates the Thuggees murdered 1 million people between 1740 and 1840.
In his 1886 book Psychopathia Sexualis, psychiatrist Richard von Krafft-Ebing noted a case of a serial murderer in the 1870s, a Frenchman named Eusebius Pieydagnelle who had a sexual obsession with blood and confessed to murdering six people.
The unidentified killer Jack the Ripper killed at least five prostitutes, and possibly more, in London in 1888. Those crimes gained enormous press attention because London was the world's greatest center of power at the time, so having such dramatic murders of financially destitute women in the midst of such wealth focused the news media's attention on the plight of the urban poor and gained coverage worldwide. He has also been called the most famous serial killer of all time.
American serial killer H. H. Holmes was hanged in Philadelphia in 1896 after confessing to 27 murders. Joseph Vacher was executed in France in 1898 after confessing to killing and mutilating 11 women and children.
In media and popular culture 
Collecting art created by convicted serial killers has become a special pastime for some. John Wayne Gacy drew and painted art from prison, much of which he gave away. Some people took the work just to trash or burn it, especially after discovering many of his images depicted his own victims. In 2005, serial killer Alfred Gaynor's art was offered on an online auction. One of his more popular works, titled "A Righteous Man's Reward", was a drawing depicting the figure of Jesus.
There is a huge market for "true crime" and mystery murder novels, some of the more successful authors being Truman Capote, Philip Carlo, Patricia Cornwell, James Patterson, Ann Rule, Harold Schechter, and Peter Vronsky. The novella Strange Case of Dr Jekyll and Mr Hyde, by Robert Louis Stevenson, can be seen as a metaphor for the complex personality of the organized serial killer type that later disintegrates into the disorganized version. One of the greatest themes of this book, however, is the possibility that the dualistic conflict seen in Jekyll/Hyde could happen to anyone. Tod Robbins' 1912 novel Mysterious Martin is an early example of a horror novel focused on a serial killer.  Other notable literature with a serial killer theme includes Bret Easton Ellis' American Psycho, Davis Grubb's The Night of the Hunter, Jim Thompson's The Killer Inside Me and Thomas Harris' books Red Dragon, The Silence of the Lambs, Hannibal and Hannibal Rising, all featuring Hannibal Lecter, a brilliant psychiatrist who is also a cannibalistic serial killer.
Since the development of film as an artform, portrayals of violence became an integral part of filmmaking. One of Thomas Edison's first phonograph recordings dealt with the confessions of serial killer H. H. Holmes. The creation of a monster helps society cope with the darker side of humanity but may lead to desensitization of media violence. The already vast and continuing production of serial-killer based works shows that the serial killer persona fascinates portions of Western culture.
Serial killers are featured as stock characters in many types of media, including books, films, television programs, songs and video games. Films featuring serial killers include M, Psycho, Henry: Portrait of a Serial Killer, The Silence of the Lambs, The Watcher, Mr. Brooks, Dirty Harry, Zodiac, Seven, The Beachcomber, Copycat, Halloween, Scream, Frailty, Man Bites Dog, The Hitcher, Monster, Kalifornia, Felidae, The Killer Inside Me Child's Play (1988 film)and many others.
One of the most well-known opponents of collectors of serial killer remnants, Andrew Kahan, is said to have coined the term "murderabilia". He is the director of the Mayor's Crime Victims Office in Houston and is backed by the families of murder victims, and "Son of Sam" laws existing in some states that prevent murderers from profiting from the publicity generated by their crimes.
Notorious and infamous serial killers number in the hundreds, and a subculture revolves around their legacies. "Murderabilia", or memorabilia centered around famous serial killers, includes the paintings, writings, and poems of these killers. Recently, marketing has capitalized even more upon interest in serial killers with the rise of various merchandise such as trading cards, action figures, and books such as The Serial Killer Files: The Who, What, Where, How, and Why of the World's Most Terrifying Murderers by Harold Schechter, and The A-Z Encyclopedia of Serial Killers by Schecter and David Everitt. Some serial killers literally attain celebrity status in the way they acquire fans, and may have previous personal possessions auctioned off on websites like eBay. A few examples of this are Ed Gein's 150-pound stolen gravestone, and Bobbie Joe Long's sunglasses.
Modern singers and bands, some more popular than others, have felt the fascination and horror toward certain celebrity serial killers, writing their own songs about them.
The television series Dexter revolves around Dexter Morgan, a police blood-spatter pattern analyst who moonlights as a vigilante serial killer, attempting to channel his homicidal urges in a "positive" direction by killing other murderers who have slipped through the cracks of the legal system. It is based on the novel Darkly Dreaming Dexter.
The television series The Mentalist has as its central antagonist a serial killer known as Red John, who until the end of the Fifth Season has murdered about 28 people, including the wife and daughter of the protagonist, the CBI consultant Patrick Jane. Discovering the identity of Red John and take revenge of him is the main goal of Jane and the series itself.
See also 
- List of horror film antagonists
- List of serial killers by country
- List of serial killers by number of victims
- Offender profiling
- Serial crime
- Son of Sam law
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- Ressler, Robert K.; Thomas Schachtman (1993), Whoever Fights Monsters: My Twenty Years Tracking Serial Killers for the FBI, New York: Macmillan/St. Martin's, ISBN 978-0-312-95044-6
- Roy, Jody M. (2002), Love to Hate: America's Obsession with Hatred and Violence, Columbia University Press, ISBN 978-0-231-12569-7
- Schechter, Harold (2003), The Serial Killer Files: The Who, What, Where, How, and Why of the World's Most Terrifying Murderers, Ballantine Books, ISBN 978-0-345-47200-7
- Schmid, David (2005), Natural Born Celebrities: Serial Killers in American Culture, University of Chicago Press, ISBN 978-0-226-73867-3
- Schmid, David (2007), Natural Born Celebrities: Serial Killers in American Culture, University of Chicago Press, ISBN 978-0-226-73869-7
- Sitpond, M. (2000), Addicted to murder: The true story of Dr Harold Shipman, Virgin Books, ISBN 0-7535-0445-6
- Tithecott, R (1997), Of men and monsters: Jeffrey Dahmer and the construction of the serial killer, Madison, Wisconsin: The University of Wisconsin Press, ISBN 0-299-15680-X
- Seltzer, Mark (1998), Serial Killers: Death and Life in America's Wound Culture, Routledge, ISBN 978-0-415-91481-9
- Vronsky, Peter (2004), Serial Killers: The Method and Madness of Monsters, Penguin Group/Berkley, ISBN 0-425-19640-2
- Vronsky, Peter (2007b), Female Serial Killers: How and Why Women Become Monsters, New York: Berkley Publishing Group, ISBN 978-0-425-21390-2
- Yudofsky, Stuart C. (2005), Fatal Flaws: Navigating Destructive Relationships with People with Disorders of Personality and Character, American Psychiatric Publishing, ISBN 978-1-58562-214-6
- Whittle, Brian; Jean Ritchie (2000), Prescription for Murder: The True Story of Mass Murderer Dr Harold Frederick Shipman, Warner
Further reading 
- DeFronzo, James; Ashley Ditta, Lance Hannon, Jane Prochnow (2007). Male Serial Homicide:The Influence of Cultural And Structural Variables. Homicide Studies, 11(1), 3-14.
- Douglas, John; Mark Olshaker (1997). Journey into Darkness. Pocket Books. ISBN 0-671-00394-1.
- Douglas, John; Mark Olshaker (1997). Mind Hunter: Inside the FBI's Elite Serial Crime Unit. Pocket Books. ISBN 0-671-01375-0.
- Douglas, John E.; Allen G. Burgess, Robert K. Ressler, and Ann W. Burgess (2006). Crime Classification Manual: A Standard System for Investigating and Classifying Violent Crimes (Second ed.). Wiley. ISBN 978-0-7879-8501-1.
- Godwin, Grover Maurice (2000). Hunting Serial Predators: A Multivariate Classification Approach to Profiling Violent Behavior. CRC Press. ISBN 978-0-8493-1398-1.
- Haggerty, Kevin D. (2009). Crime, Media, Culture: Modern Serial Killer. Sage 5(2), 1-21.
- Holmes, Ronald M.; Stephen T. Holmes (2001). Sex Crimes: Patterns and Behavior (Second ed.). Sage. ISBN 978-0-7619-2417-3.
- Holmes, Ronald M.; Stephen T. Holmes (2002). Profiling Violent Crimes: An Investigative Tool. Sage. ISBN 978-0-7619-2594-1.
- Lane, Brian (2006). The New Encyclopedia Of Serial Killers (2nd ed.). Facts On File. ISBN 0816061955.
- Leyton, Elliott (1986). Hunting Humans: The Rise of the Modern Multiple Murderer. McClelland & Stewart. ISBN 0-7710-5025-9.
- MacDonald, J. M (1963). The threat to kill American Journal of Psychiatry. American Psychiatric Association. Retrieved 2011-05-31.
- Newitz, Annalee (2006). Pretend We're Dead: Capitalist Monsters in American Pop Culture. Duke University Press. ISBN 978-0-8223-3745-4.
- Norris, Joel (1990). Serial Killers: The Growing Menace. Arrow Books. ISBN 0-09-971750-6.
- Ramsland, Katherine (2007). Inside the minds of healthcare serial killers : why they kill. Praeger. ISBN 978-0-275-99422-8.
- Ramsland, Katherine; Karen Pepper. "Serial Killer Culture". Tru.tv Crime Library. Retrieved April 2, 2010.
- Robinson, Bryan. "Serial Killer Action Figures For Sale". ABC News. Retrieved April 1, 2010.
- Rosner, Lisa (2010). The Anatomy Murders. Being the True and Spectacular History of Edinburgh's Notorious Burke and Hare and of the Man of Science Who Abetted Them in the Commission of Their Most Heinous Crimes. University of Pennsylvania Press. ISBN 0-8122-4191-6.
- Rushby, Kevin (2003). Children of Kali: Through India in Search of Bandits, the Thug Cult, and the British Raj. Walker & Company. ISBN 0-8027-1418-8.
- Schlesinger, Louis B. (2000). Serial Offenders: Current Thought, Recent Findings. CRC Press. ISBN 978-0-8493-2236-5.
- Vronsky, Peter (2004). Serial Killers: The Method and Madness of Monsters. Penguin Group/Berkley. ISBN 0-425-19640-2.
- Wilson, Colin (1995). A Plague Of Murder. Constable & Robinson. ISBN 1-85487-249-4
|Wikimedia Commons has media related to: Serial killers|
- Crime Library's Serial Killer page
- Serial Murder: Multi-Disciplinary Perspectives for Investigators Official FBI publication