Editor’s Note: This story contains discussions of rape or sexual assault that may be disturbing. Reader discretion is advised. If you or someone you know has been sexually assaulted, you can find help and discreet resources on the National Sexual Assault Hotline website or by calling 1-800-656-4673.
(NewsNation) — Serial killers have always been a subject of interest for many — how do their brains work? How common are serial killers?
According to Britannica, a serial killer is a person who kills at least two people in different events at different times. PsychologyToday says that while motives aren’t always clear, typically serial killers will share “abnormal psychological processes.” This can include having an extreme tendency to be antisocial.
Despite the definition from Britannica, some experts would disagree. Some say that a serial killer is a person who has killed three people over a span of more than one month. Some will go further and say that serial killers must have a motive, like sexual gratification, that isn’t just about the murders themselves.
In 2005, the Federal Bureau of Investigation said that fewer than 1% of homicides during a year were committed by serial killers, making them pretty rare.
Most well-known serial killers
Some of the most well-known serial killers include:
Ted Bundy
Ted Bundy is probably one of, if not the most, well-known serial killer in U.S. history. Bundy sexually assaulted and killed several younger women between 1974 and 1978. He killed women in Washington, Oregon, Colorado, Utah and Florida.
(Original Caption) Suspected murderer Theodore Bundy, charged with the killings of FSU coeds Margaret Bowman and Lisa Levy who were beaten and strangled at the Chi Omega House in January, is shown in this photograph. (Credit: Bettmann / Contributor) 
(Original Caption) Florida State University’s Chi Phi fraternity celebrates the execution of Ted Bundy with a large banner that says, “Watch Ted Fry, See Ted Die!” as they prepare for an evening cookout where they will serve “Bundy burgers” and “electrified hot dogs.” Bundy attacked five women and killed two Chi Omega coeds on the campus in 1978. Bundy died in the electric chair, 1/24. (Credit: Bettmann / Contributor) 
Ted Bundy’s image on a television screen on the lawn of the Florida State Prison. | Location: Starke, Florida, USA. (Credit: Bettmann / Contributor) 
(Original Caption) Miami, FLA.: Theodore Bundy, seated in court, charged with the killings of two FSU coeds. (Credit: Bettmann / Contributor)
He eventually confessed to 28 murders, however, some have estimated that he could be responsible for hundreds of deaths. After his trial, he was sentenced to death in 1979 for killing two college students. Then, in 1980, he was sentenced to death again for the rape and murder of a 12-year-old girl. In 1989, Bundy was executed by electric chair in Florida.
While he was in custody in 1977, he had even escaped, causing the FBI to release a wanted poster and search for him until he was found.
Pedro Lopez
Also known as the “Monster of the Andes,” Pedro Lopez targeted young women from Peru and Ecuador. In his early life, he dealt with homelessness, violence and sexual abuse, and was arrested at a young age. In 1980, he was arrested and charged with 110 murders. He pleaded guilty to all of those murders.
Lopez served 14 years in prison before he was deported to Colombia. In Colombia, police tried to convict him for a murder that was two decades old, but he was declared insane and put into a psychiatric facility in 1995.
However, in 1998, it was decided that he was sane, and he was released with a $50 bail. When he was released, he allegedly visited his mother, asked for his inheritance, and sold her bed and chair when he was told she was in poverty. Lopez vanished and hasn’t been seen since.
H.H. Holmes
H.H. Holmes is believed to be the United States’ first known serial killer. In 1886, Holmes, whose original name was Herman Mudgett, took a job as a pharmacist in Chicago. At this point, he changed his name to Dr. H.H. Holmes.
Holmes built his own house, equipping it with secret passages, trapdoors, soundproof rooms, doors that would lock from the outside, and more. This would later be known as his “Murder Castle.” In 1893, he allegedly killed many women, normally by getting engaged to them and only killing them after getting control of their life savings.
Holmes’ employees allegedly had to carry life insurance policies that listed him as a beneficiary so he could collect the money after he killed them. He also sold the bodies of his victims to medical schools. Holmes eventually admitted to committing 27 murders, but he later increased that number to more than 130. Some researchers believe the real number could be closer to 200.
John Wayne Gacy
John Wayne Gacy was arrested in Illinois in 1979 for a number of killings in the Des Moines, Illinois, area. According to the FBI, Gacy was convicted in 1980 for killing 33 men, with the youngest being 14 years old and the oldest being 21 years old.
Gacy had been known in his community for hosting parties and dressing up as Pogo the Clown. In 1976, police tried to connect Gacy to the disappearance of a 9-year-old boy. However, they weren’t able to make the case. In 1977, Jeff Rignall had accused Gacy of using chloroform to render him unconscious and then sexually assaulting him.
John Wayne Gacy 
John Wayne Gacy, 36, taken from the Des Plaines Police Station en route to a hospital, on Dec. 23, 1978. (William Yates/Chicago Tribune/Tribune News Service via Getty Images) 
The backyard structures have been completely demolished and the yard dug up at the home where John Wayne Gacy lived and killed 33 people in Norwood Park Township. This view, taken on March 19, 1979, shows the back of the house. (Walter Kale/Chicago Tribune/Tribune News Service via Getty Images) 
John Wayne Gacy’s house at 8213 W. Summerdale Avenue in Norwood Park at the time of his arrest on Dec. 22, 1978. (William Yates/Chicago Tribune/Tribune News Service via Getty Images) 
John Wayne Gacy, 36, is removed from the Des Plaines Police Station en route to a hospital on Dec. 23, 1978. (William Yates/Chicago Tribune/Tribune News Service via Getty Images) 
At the Des Plaines police station, John Wayne Gacy covers his face with his manacled hands as he emerged after an all-night questioning session on Dec. 22, 1978. (Roy Hall/Chicago Tribune/Tribune News Service via Getty Images)
A civil suit for $3,000 had been settled in court, and Gacy had also been charged with battery. At the end of 1978, Gacy was eventually arrested for numerous crimes. He had allegedly told his lawyer that he had committed “maybe 30” murders. When searching his home, police found a trapdoor that led to a crawl space. In that space, they found body parts of at least three people.
In 1979, Gacy was charged with the murder of seven men. He was also charged with several felonies, including aggravated kidnapping and deviate sexual assault. He pleaded not guilty, but a few months later, he was indicted for an additional 26 murders.
In 1980, after five weeks of trial, a jury took less than two hours to find Gacy guilty of killing 33 people. On May 10, 1994, Gacy was executed by lethal injection in Illinois.
Harold Shipman
Harold Shipman was a doctor in England who allegedly killed nearly 250 of his patients. After becoming a general practitioner, it was found that he was writing false prescriptions for opiate pethidine, which he had become addicted to. He was forced out of the practice where he worked and into rehab.
He eventually became a general practitioner again in 1977, with one of his patients being found dead in her home after Shipman had visited her in 1998. Her will had been changed to benefit Shipman, and Shipman told officials that no autopsy was needed.
Shipman was eventually convicted on 15 counts of murder and one count of forgery in 2000. He was sentenced to life in prison, but committed suicide by hanging himself in his cell. A government inquiry that was completed in 2005 found that Shipman had actually killed nearly 250 people, starting in 1971.
Jeffrey Dahmer
Jeffrey Dahmer is well-known in the U.S., committing his first murder in Ohio in 1978. Over the next few years, he killed around 16 people, mostly young men who were in poverty and African American, Asian or Latino.
According to the FBI, there were eventually 11 victims’ remains found in Dahmer’s apartment. Soon after he was arrested, he confessed to killing more than a dozen people, including torturing and mutilating his victims and abusing their corpses.
Dahmer was sentenced to life in prison and extradited to Ohio, where he was convicted of killing another person. While he was serving his life sentence, he was killed by a fellow inmate in 1994 in a Wisconsin prison.
Jack the Ripper
Jack the Ripper has been accused of killing at least five women in London in 1888. This is one of the most famous unsolved cases in London’s history. It was believed at the time that these women were prostitutes and all but one were killed while soliciting on the street.
In each killing, the victim’s throat was cut, and the body was mutilated. On one occasion, half of a human kidney was mailed to the police.
A historian recently claimed to have discovered the real identity of Jack the Ripper. Through DNA matching, the historian claims that 23-year-old Aaron Kosminski was Jack the Ripper. He had been considered a suspect for a long time during the investigations.