|Note: Varies by jurisdiction|
|Assassination · Child murder
Contract killing · Felony murder rule
Honour killing · Human sacrifice
Lust murder · Lynching
Mass murder · Murder–suicide
Proxy murder · Lonely hearts killer
Serial killer · Spree killer
Torture murder · Feticide
Double murder · Misdemeanor murder
Crime of passion · Internet homicide
|in English law
|Note: Varies by jurisdiction|
|By victim or victims|
A serial killer is a person who murders three or more people over a period of more than thirty days, with a "cooling off" period between each murder, and whose motivation for killing is largely based on psychological gratification. Often, a sexual element is involved with the killings. 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 often confused with being mass murderers, which are defined by multiple murders that are committed at one time. Coinage of the English term serial killer is commonly attributed to former FBI Special Agent Robert Ressler in the 1970s. The concept had been described earlier, e.g. by German police inspector Ernst Gennat coining the same term in 1930. 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, mastermind of the ViCAP system.
Psychosis is rarely noted among serial killers. The predominant psychiatric diagnosis noted in the group tends toward the psychopathic, meaning they suffer from traits within a specific cluster of dysfunctional personality characteristics, those most commonly associated with Antisocial Personality Disorder or Dissocial personality disorder. Psychopaths lack empathy and guilt, are egocentric and impulsive, and 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 named the "mask of sanity".
The FBI's Crime Classification Manual places serial killers into three categories: "organized", "disorganized" and "mixed"—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 123. They often plan their crimes quite methodically, usually abducting victims, killing them in one place and disposing of them in another. They will 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 metal bar (e.g. a crowbar), 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 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. Ted Bundy and John Wayne Gacy are examples of organized serial killers.
Disorganized asocial offenders are often of low intelligence, have a below average IQ (<90), and commit their crimes impulsively. Whereas the organized killer will specifically set out to hunt a victim, the disorganized will murder someone when the opportunity arises, rarely bothering to dispose of the body but instead just leaving it at the same place where they found the victim. They usually carry out blitz-style attacks, leaping out and attacking their victims without warning, and will typically perform whatever rituals they feel compelled to carry out (e.g., necrophilia, mutilation, cannibalism, etc.) once the victim is dead. They rarely bother to cover their tracks but may still evade capture for extended periods of time due to the anonymous nature of the crime. They are often introverted, socially inadequate with few friends, and they may have a history of mental problems. Richard Chase is an example of a disorganized serial killer.
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 an earthquake. As the war wound down, Mullin claimed his father instructed him via telepathy to raise the amount of "human sacrifices to nature" in order to delay a catastrophic earthquake that would plunge California into the ocean.
Mission-oriented killers typically justify their acts as "ridding the world" of a certain type of "undesirable" person, such as homosexuals, prostitutes, blacks or Catholics; however, they are generally not psychotic. Some see themselves as attempting to change the nature of human society, often to cure a societal ill. 
Ted Kaczynski, the "Unabomber", targeted universities and the airline industry. He wrote a manifesto that he distributed to the media, in which he claimed he wanted society to return to a time when technology was not a threat to its future, asserting that "the Industrial Revolution and its consequences have been a disaster for the human race."
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. 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. 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 create 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. Lee Boyd Malvo and John Allen Muhammad, the DC Snipers, killed random victims, often at gas stations, shooting them and leaving the scenes unnoticed. 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.
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 ("hit men") may also be considered serial killers.
Some, like Puente and Holmes, may be involved in and/or have previous convictions for theft, fraud, dishonesty, 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.
Their main objective for killing 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.
Some people with a pathological interest in the power of life and death tend to be attracted to medical professions. These kinds of killers are sometimes referred to as "angels of death" or angels of mercy. One example is Harold Shipman, an English family doctor, who made it appear that his victims died of natural causes (disease). Between 1975 and 1998, he murdered at least 215 patients; he is suspected of having murdered 250 people. Dr John Bodkin Adams, meanwhile, though acquitted in 1957 of the murder of one patient, is believed to have killed around 163 patients in Eastbourne, England.
A number of medical murderers were involved in fraud. For example, H. H. Holmes was often involved in insurance scams and confidence tricks. Harold Shipman had a previous conviction for prescription fraud and forgery, for which he was fined £600.
Criminologists have long recognized that there are links between most serial killers and their chosen victims. Demographically, serial murderers tend to target more women than men, and kill strangers more often than family or acquaintances, as opposed to single-homicide offenders, who tend to kill men and women equally, while killing friends and family more often.
Serial murderers’ killings are often sexually motivated, although there are exceptions. The sexual motivation supports the theory that serial murderers tend to have specific criteria and specific sexual interests that motivate their selection of certain victims. This victim selection process sets serial murderers apart from other types of killers. Gay serial killers, such as Jeffrey Dahmer or Dennis Nilsen, often killed other gay men.
In the United States, serial killers prefer to target victims ages 18–50. The majority of victims are white, supporting researchers' claims that serial murder is intra-racial.
Female serial killers tend to kill those with whom they are already intimately familiar, as opposed to men who usually target strangers. "For female serial killers, historically husbands and their children are first choice as victims. When comparing males who kill children versus women, women kill children at a much higher percentage. The percentage of offenders killing at least one type of victim who is a child, males are at 21% whereas women are at 39%."
Female serial killers are rare. They tend to murder men for personal gain, are usually emotionally close to their victims, and generally need to have a relationship with a person before killing them. "An analysis of 86 female serial killers from the U.S. found that the victims tended to be spouses, children or the elderly." The methods they use for murder are covert or low-profile, such as murder by poison. They commit killings in specific places, such as their home or a health-care facility (where they then become known as "Angels of Mercy" by the media), or at different locations within the same city or state. Each killer will have her own proclivities, needs and triggers, as specific reasons can only be obtained from the killer herself. On rare occasions, women may be involved with a male serial killer as a part of a serial killing "team".
"In a review of published literature on female serial murder, the most common motive identified was material gain." 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. In a study of 105 female serial killers, the preferred method of killing was poisoning.
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. Another atypical female serial murderer 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.
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.
Liu Pengli of China, cousin of the Han Emperor Jing, was made king 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, and Liu Pengli was made a commoner and banished.
In the 15th century, one of the wealthiest men in Europe, 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 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. Recent scholarship has cast doubt on the Thuggee cult and suggested that the British in India were confused by the vernacular use of the term by Indians, and may also have used fear of such a cult to justify their colonial rule.
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 prostitutes (the exact number of victims is not known) in London in 1888. Those crimes gained enormous press attention because London was the world's greatest centre 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.
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 Psycho, The Silence of the Lambs, Hannibal, Mr. Brooks, Seven, Copycat, Halloween, Scream and many others.
The television series Dexter features a police blood-spatter pattern analyst who moonlights as a vigilante serial killer who goes after criminals who have slipped through the law's fingers in an attempt to be "good". It is based on the novel Darkly Dreaming Dexter. Other notable literature with a serial killer theme includes Davis Grubb's The Night of the Hunter, Norman Mailer's The Executioner's Song, Bret Easton Ellis' American Psycho, 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.
A serial killer is someone who murders several people at different times (similar killers of more than one person are mass murderers and spree killers). The victims are usually people the serial killer does not know, and the killer commits his crimes to get a certain kind of excitement or other feeling. He usually has no practical motive such as robbery or revenge.
Serial killer first became a commonly used phrase for this kind of killers in the 1970s. This was the result of the crimes of people like Ted Bundy and David Berkowitz ("Son of Sam"). Jack the Ripper is thought by many to be one of the first serial killers that many people knew about, even though his victims were killed long before the phrase was invented.
A serial killer's crimes are nearly always alike in some ways. The killer may only attack a certain type of person, for instance women of a certain age or appearance (young or old, blonde or dark-haired). He may always use the same kind of weapon to kill his victims, or may treat them in a certain manner, such as tying them up with the same kind of rope or adhesive tape. Some serial killers have had very strange habits which leave evidence of their work at each crime; for instance Albert de Salvo, the Boston Strangler, would tie the cord with which he had strangled a woman around her neck in a special bow. To law enforcement officers a serial killer's habits are known as his signature, and they are always valuable leads in detecting who he is and capturing him.
Some of the worst serial killers have been doctors. Harold Shipman, a British general practitioner, is thought to have killed up to 250 of his patients. John Bodkin Adams, also British, is thought to have killed 163 patients.