While evidence of serial killers has been found widely across cultures and in records dating back to B.C., public interest in them has only arisen within the past few centuries. A litany of shows, films, documentaries, podcasts and even museums have been dedicated solely to exploring the horrors of serial murders and the people behind them.

The the National Institute of Justice defines serial killers are people who commit two or more murders with a psychological motive and, occasionally, sadistic, sexual overtones. In the case of male serial killers — the most common kind — these sexual overtones typically involve the exertion of dominance over their victims. Yet for female serial killers, these sexual overtones can be replaced by what Dr. Berit Brogaard of Psychology Today describes as “a twisted sense of love, sympathy, or altruism.” The FBI has claimed that this public interest in serial killers is a phenomenon much like the one following the murders of Jack the Ripper in 19th century London. But why exactly is the general population so invested in this type of violence? Why do people love learning about brutal killings at the hands of psychopathic murderers?

The answer is actually quite simple. For many serial killer enthusiasts, it’s the rush of excitement that comes with learning about a murder. One’s palms might get sweaty, and they may start feeling their heart beat faster and faster. The registered horror sends a dose of dopamine straight to the brain — a hormone that can be released during times of pleasure or fear. Not only that, exploring violent or disturbing subjects is common through media because people feel safe and detached from the realistic horror of it.

According to a 2014 study by Bridget Rubenking and Annie Lang that examined core and sociomoral disgusts in entertainment media, while participants who were shown videos that portrayed death and gore reacted negatively, the videos also provoked strong indications of arousal and attention in their brains. This data supports the notion that humans are not only attracted to things that we find appealing or pleasurable, but also to things that we find repulsive or “unthinkable.”

Something else we find so fascinating about serial killers is the psychological patterns that many of them seem to share. An average human being possesses the ability to feel and perceive empathy, shame, remorse, pity, etc. It’s difficult to imagine what it’s like to not feel these emotions, and to examine psychopathic behavior — often associated with serial killers — is interesting because it presents a different sense of danger that makes us question our safety.

Dr. Scott A. Bonn of Psychology Today believes there are six main reasons why the public is so fascinated with serial killers: 1) they’re rare criminals, seemingly exotic and extreme to the average person, 2) they choose their victims randomly, leading one to question their safety, 3) serial killers are described as “insatiable”, 4) it’s difficult to comprehend the violent thought process of serial killers, who kill without coherent motives like jealousy or rage, 5) they provide a euphoric adrenaline rush to audiences, much like monsters in horror movies, and 6) they are an outlet for one to explore primal feelings such as fear, anger, and lust.

The 1970s and 80s were an active time period for serial killers, with over 500 reported serial murders committed in the 70s and just over 600 in the 80s. Since then, these criminals have reached somewhat of a celebrity status in American culture. Whether through fictional depictions in television and film — “Dexter”, “Silence of the Lambs” — or through documentary-style programs — “Aileen: The Life and Death of a Serial Killer”, “The Jeffrey Dahmer Files” — their atrocities have become a source of entertainment in American culture.

Through these mediums we’ve often tried to humanize serial killers, while also noting them as a clear demarcation between good and evil. In some cases, there are individuals — particularly women — who find themselves especially attracted to high-profile serial killers and send them fan mail, or visit them in prison. These serial killer “groupies” are often referred to as hybristophiliacs — people who are sexually attracted to individuals that have committed violent and gruesome crimes such as murder or rape.

Ultimately, many of us — even those who aren’t looking to start up a relationship with a local serial killer — still find them fascinating, despite their repulsive history and behavior. There’s a reason why so many call serial killer programs their “guilty pleasure”, and why movies often base their villainous characters on them. Serial killers have made an impact on culture that helps us define the boundaries between good and evil, thus providing more to society than any of us probably thought they would.