How Serial Killers Work

By: Shanna Freeman

murder serial killer
What makes a person not only murder, but murder multiple people over periods of days, weeks and years? D-Keine / Getty Images

­The Zodiac Killer. John Wayne Gacy. The BTK Killer. Ted Bundy. Son of Sam. Jeffrey Dahmer­. The names and pseudonyms of these killers are burned into the collective consciousness of Americans, thanks to massive coverage in newspapers, books, films and TV specials. Many of those who have been captured appeared average -- attractive, successful, active members of the community -- until their crimes were discovered.

This kind of killer doesn't just "go crazy" one day and kill a lot of people. He doesn't kill out of greed or jealousy. So what makes a person not only murder, but murder multiple people over periods of days, weeks and years? There's a special name for these types of murderers: serial killers. In this article, we'll learn about what makes them tick.


The term "serial killer" was coined in the mid-1970s by Robert Ressler, the former director of the FBI's Violent Criminal Apprehension Program. He chose "serial" because the police in England called these types of murders "crimes in a series" and because of the serial films that he grew up watching. Prior to this, these types of crimes were sometimes known as mass murders or stranger-on-stranger crime.

The FBI defines a serial killer as one who murders three or more victims, with "cooling-off" periods between each murder [source: U.S. Code]. This sets them apart from mass murderers, who kill four or more people at the same time (or in a short period of time) in the same place, and spree killers, who murder in multiple locations and within a short period of time. Serial killers usually work alone, kill strangers and kill for the sake of killing (as opposed to crimes of passion).

According to a recent FBI study, there have been approximately 400 serial killers in the United States in the past century, with anywhere from 2,526 to 3,860 victims [source: Hickey]. However, there's no way to really know how many serial killers are active at any point in time -- experts have suggested numbers ranging from 50 to 300, but there's no evidence to support them.

Serial murders also appear to have increased over the past 30 years. Eighty percent of the 400 serial killers of the past century have emerged since 1950 [source: Vronsky]. Why this is happening is a question of some debate; there is no answer, just as there is no simple answer as to why some people become serial killers.

In the next section, we'll look at some classifications of serial killers in use by criminal researchers and profilers so we can begin to understand this phenomenon.

Serial Killer Classifications

­Intense study in the field of serial murder has resulted in two ways of classifying serial killers: one based on motive and one based on organizational and social patterns. The motive method is called Holmes typology, for Ronald M. and Stephen T. Holmes, authors of numerous textbooks on serial murder and violent crime. Not every serial killer falls into a single type, and many are more than one type. Neither of these classifications explain what might actually lead someone to become a serial killer (more on this later). There is not enough scientific data upon which to base these classifications, either -- they are based on anecdotal and interview data. Critics of the Holmes typology point to this as a flaw, but many investigators still find the method useful when studying serial murder.

­Acc­ording to Holmes typology, serial killers can be act-focused (who kill quickly), or process-focused (who kill slowly). For act-focused killers, killing is simply about the act itself. Within this group, there are two different types: the visionary and the missionary. The visionary murders because he hears voices or has visions that direct him to do so. The missionary murders because he believes that he is meant to get rid of a particular group of people.


Process-focused serial killers get enjoyment from torture and the slow death of their victims. These include three different types of hedonists -- lust, thrill and gain -- and power-seeking killers. Lust killers derive sexual pleasure from killing. Thrill killers get a "kick" from it. Gain killers murder because they believe they will profit in some way. Power killers wish to "play God" or be in charge of life and death.

Serial Killer Behavior

Serial killers can also be classified by their organizational and social skills. They can be organized or disorganized (depending on the type of crime scene) and nonsocial or asocial (depending on whether they are excluded by society or exclude themselves). The following chart illustrates behaviors of the two most common types.

The majority of identified serial killers are organized and nonsocial. Most of them also follow some other basic patterns. More than 80 percent of serial killers are male, Caucasian and in their 20s or 30s [source: Hickey]. Serial killers are generally intelligent, and they usually kill Caucasian women. There's no way to "tell" a serial killer simply by his appearance -- most of them look like everyone else. Ted Bundy, who was convicted of 30 murders, was often described as attractive, charismatic and articulate. John Wayne Gacy was a popular figure in his community and often performed as a clown at block parties. He met with first lady Rosalynn Carter when he was precinct captain of his local Democratic Party. He was also convicted of the murders of 33 boys and men.


Often, serial killers exhibit three behaviors in childhood known as the MacDonald triad: bed-wetting, arson and cruelty to animals. They are also likely to have come from broken homes and been abused or neglected. Although some are shy and introverted, others are gregarious and outgoing but actually feel very isolated.

Many theorists point to the troubled childhoods of serial killers as a possible reason for their actions. We'll explore this and other theories for why they do it in the next section.

Serial Killer Motives

Jeffrey Dahmer at his trial in 1991. He killed at least 17 men and boys.
Jeffrey Dahmer at his trial in 1991. He killed at least 17 men and boys.
Eugene Garcia/AFP/Getty Images

One of the most studied aspects of serial murder is “why?” A number of theories have been set forth as potential explanations. But “unraveling the making of a serial killer is like aligning a Rubik's cube” [source: Vronsky]. In other words, there is no one answer. Let's take a look at three possible theories: childhood neglect and abuse, mental illness and brain injury.

Neglect and Abuse

One theory centers around the neglect and abuse that many serial killers experience as children. Robert Ressler and Tom Shachtman describe a study conducted by the FBI, which included interviews with dozens of murderers (mostly serial killers). In each case, they found “similar patterns of severe childhood neglect” [source: Ressler & Shachtman]. During a child's development, there are important periods in which he learns about love, trust, empathy and basic rules about how to interact with other human beings. If these traits aren't imprinted upon the child during that period, it may not be possible for him to learn them later in life.


Serial killers were often physically or sexually abused as children or witnessed the abuse of family members. This pattern of neglect and abuse, some researchers say, leads serial killers to grow up without a sense of anyone other than themselves. But at the same time, many children grow up neglected and abused, but do not become violent criminals or serial killers.

On the next page we'll learn about mental illness and brain injury in serial killers.

Serial Killer Sanity

­For some people, the only way to explain serial murder is to say that serial killers are "insan­e." Some serial killers do plead "not guilty by reason of insanity" as a defense, but are all of them "insane" or even mentally ill? According to the U.S. Code, an insanity defense means that "at the time of the commission of the acts constituting the offense, the defendant, as a result of a severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of his acts. Mental disease or defect does not otherwise constitute a defense" [Source: U.S. Code].

Basically, a serial killer arguing "not guilty by reason of insanity" must prove that he did not understand right from wrong at the time that he killed. But it can be difficult to prove that he really did not understand that his actions would result in the death of the victims. Only two serial killers have successfully pled insanity. John Douglas, long-term head of the FBI's Investigative Support Unit, believes that serial killers "don't have a problem understanding what death means, and that they have the power to kill" [source:].


Some serial killers have been diagnosed by psychologists and psychiatrists as psychopaths. The official term in the Diagnostic and Standard Manual of Mental Disorders, fourth edition (DSM-IV) is antisocial personality disorder (APD). According to the DSM-IV, a person with APD follows a pattern of "disregard and violation of the rights of others occuring since age 15 years." This pattern includes seven factors (three of which must be met for diagnosis), such as "failure to conform to social norms," "irritability and aggressiveness" and "lack of remorse" [source: Vronsky]. Psychopaths are not insane -- they do know right from wrong. But this diagnosis may explain their behavior during their killing cycles.

Brain Injury

Some researchers theorize that serial killers have brain damage or other biological abnormalities that contribute to their actions. Damage to areas like the frontal lobe, the hypothalamus and the limbic system can contribute to extreme aggression, loss of control, loss of judgment and violence. Henry Lee Lucas, who was convicted of 11 murders, was shown to have extreme brain damage in these areas, probably the result of childhood abuse, malnutrition and alcoholism. Arthur Shawcross, another 11-time serial killer, was found to have had several brain injuries, including two skull fractures. While in prison, he suffered from headaches and often blacked out. Bobby Joe Long, convicted of nine murders, stated at one point, "After I'm dead, they're going to open up my head and find that just like we've been saying a part of my brain is black and dry and dead" [source: Scott].

In the next section, we'll see how law enforcement catches serial killers.

Catching a Serial Killer

Investigators search for the remains of a victim of Gary Ridgway, the Green River Killer.
Investigators search for the remains of a victim of Gary Ridgway, the Green River Killer.
King County Prosecutor's Office/Getty Images

A serial killer keeps killing until one of four things happens: he is caught, he dies, he kills himself or he burns out. Obviously once law enforcement determines that a string of murders can be attributed to one person, the goal is to catch him as soon as possible. But how do they figure this out? And how are serial killers caught?

­In the aftermath of any homicide, inv­estigating the crime scene and performing an autopsy are routine steps that law enforcement takes in an attempt to solve the crime. Once all of this information has been collected, it can be entered into a nationwide database run by the FBI, as part of ViCAP (Violent Criminal Apprehension Program). This program can help to determine patterns, or signatures, that link separate homicides.


According to FBI profiler John Douglas, a signature "is a ritual, something the subject does intentionally for emotional satisfaction -- something that isn't necessary to perpetuate the crime” [source:]. Some serial killers pose their victims in a certain way or leave them in a certain place after killing them. Another signature might be a method of torture or mutilation. It's what the killer does to fulfill his fantasies, and it can tell investigators a lot about his personality.

Investigators also look at the MO, or modus operandi, of the crime. The MO reflects what the killer had to do to commit the crime. This includes everything from luring and restraining his victim to the way that he actually murders her. A serial killer's MO can change over time. Essentially, he learns from past mistakes and improves with time.

Serial Killer Profiling

Ed Gein, the inspiration forthe Buffalo Bill character in­"The Silence of the Lambs"
Ed Gein, the inspiration forthe Buffalo Bill character in­"The Silence of the Lambs"
Francis Miller/Time & Life Pictures/

Determining the signature and the MO are both aspects of profiling. The FBI's Behavioral Sciences Unit developed the process of profiling in the 1970s, and Ted Bundy was one of the first serial killers to be profiled. Studies by psychologists and psychiatrists and information gleaned from past serial murders go into the creation of the profile, along with crime-scene information and witness statements. For example, if the victim is Caucasian, the killer is probably Caucasian. If the crime scene shows evidence of careful planning, the killer is likely to be intelligent and older. If the victim was mutilated in a very disorganized way, her killer is probably schizophrenic, and schizophrenics are more likely to be very thin and unkempt [source: Vronsky].

Profiles are not 100 percent accurate, but they're usually found to be very close. According to Robert Keppell, the detective who took Bundy's confession, the profile assembled for Bundy's crimes was perfect, "even to the point where they predicted he'd have a step-brother and that's what he had" [source: Bellamy].


Once the profile is completed, investigators can look at the existing list of suspects and determine which are most likely to have committed the crime and determine how best to capture him. Some organized serial killers, such as Dennis Rader (the BTK Killer), feel the need to taunt the police, which sometimes leads to their arrest. Rader sent police a floppy disk containing metadata that was traced to his church. Many serial killers, even those who are incredibly organized and methodical, slip up in some way that leads to their arrest. In the case of Jeffrey Dahmer, a potential victim escaped and led police to Dahmer's apartment. Some of John Wayne Gacy's victims had worked for his construction business.

But not all serial killers are caught. Some are arrested or picked up for other crimes, and evidence leads investigators to their murders. Ted Bundy was caught at a routine traffic stop, while David Berkowitz, the "Son of Sam," was initially picked up for loitering and was thought to be a witness to the crimes instead of the killer.

Once convicted, most serial killers either spend their lives in prison or are executed if the death penalty exists in their state. Ed Gein is one exception. At first found incompetent to stand trial, Gein was sent to a mental institution. Later his psychiatrist determined that he was competent, and a judge found him not guilty by reason of insanity. Gein died in 1984 of heart failure.

Most researchers agree that there is no way to "cure" a serial killer. Some serial killers who spent time in mental institutions after committing their crimes or received psychiatric treatment were deemed "cured" and released, but they went on to kill again. Others did not improve after a number of treatment attempts. Peter Woodcock spent 35 years in a criminal psychiatric hospital in Ontario, Canada, after murdering three children. While out on a day pass, he and his security guard escort -- who was also a previously imprisoned killer -- killed another patient.

Until we know more about how to stop serial killers before they start to kill or refine ways of capturing them before they continue the cycle of murder, they will continue to be as much a part of reality as murder itself.

For lots more information about serial killers and related topics, check out the links on the next page.

Lots More Information

Related Articles

More Great Links

  • Bellamy, Patrick. "On the Trail of Ted Bundy." The Crime Library.
  • Douglas, John. "Violent Predators Hide Behind the Insanity Defense But They Know the Difference Between Right and Wrong." John Douglas: Mind Hunter.
  • Douglas, John. "Linking Cases Together: Following a Killer's Signature." John Douglas: Mind Hunter.
  • "Green River Killer avoids death in plea deal.", November 5, 2003.
  • Hickey, Eric W. "Serial Murderers and Their Victims." Wadsworth/Thomson Learning, 2002.
  • Holmes, Ronald M. and Stephen T. "Profiling Violent Crimes." Sage Publications, 2002.
  • Karr-Morse, Robin and Meredeith S. Wiley. "Ghosts From the Nursery: Tracing the Roots of Violence." Atlantic Monthly Press, 1997.
  • "Murder - Crime in the United States 2004." FBI.
  • O'Connor, Tom. "Serial Killer Typology." MegaLinks in Criminal Justice. January 23, 2006.
  • O'Neil, Dennis. "Sex Chromosome Abnormalities." Behavioral Sciences Department, Palomar College, January 1, 2007.
  • Ressler, Robert K. and Tom Schactman. "Whoever Fights Monsters." St. Martin's Press, 1993.
  • Rhodes, Richard. "Why They Kill." Knopf, 1999
  • Scott, Shirley Lynn. "What Makes Serial Killers Tick?" The Crime Library.
  • U.S. Code. Title 18. Part 1, Chapter 1, Section 17 - Insanity Defense.
  • U.S. Code. Title 28. Part II, Chapter 33, Section 540B - Investigation of Serial Killings.
  • ViCAP: FBI Investigative Programs Critical Incident Response Group.
  • Vronsky, Peter. "Serial Killers: The Method and Madness of Monsters." Berkley Books, 2004.