Sadly, tales of domestic violence zoom in and out of the news so frequently that they rarely capture the public’s attention, and when they do, they don’t hold it for long. Meanwhile, Gacy’s story, along with those of other serial killers like Ted Bundy, Jeffrey Dahmer, and David Berkowitz, are remembered even decades later: They’re so well-known that we continue to hear casual references to them in pop culture. For example, in Katy Perry’s recent song “Dark Horse,” Juicy J raps, “She’ll eat your heart out/like Jeffrey Dahmer.” Dahmer, who was known for cannibalizing his victims, committed his crimes between 1978 and 1991, and was killed in prison in 1994, nearly 20 years before “Dark Horse” was released.

Juicy J can drop that tasteless reference and know it will be understood because serial killers are “still very much a part of our culture,” Penman says. The question is, why? What draws people to their dark, disturbing stories? Why do some killers become celebrities while others are forgotten?

In his new book, Why We Love Serial Killers (out October 28), criminologist Dr. Scott Bonn attempts to solve some of these mysteries. “My question is: What can we learn from these individuals?” he says. “What can we learn about ourselves? People are drawn to understanding the dark side, and the dark side is part of the human condition.”

This desire to see into the mind of a serial killer can be a powerful attraction. At the Crime Museum, I met a 59-year-old tourist named Joanne Marvel who described her lifelong fascination with crime. A recording of a police siren blared around us as she told me how her grandfather used to read crime magazines, and how her father claimed to have met Al Capone once in Chicago during the heyday of organized crime. “For me it’s about how their childhood affected what they did later,” Marvel said. “I think a lot of people think that way—they want to know why [the killer] got that way rather than what he did. It’s more about why he did it.”

As retired NYPD homicide detective Dave Carbone told Bonn when asked about the public’s interest in serial killers, “The why is the wow.” Or in the words of Katherine Ramsland, a forensic psychologist and author of numerous books including The Human Predator, “It’s not really about the victims. It’s more about the puzzle—the interesting labyrinth of human emotions and human motives.”

What made serial killers this way? Why did they kill, and why did they do it so gruesomely? How are they different from us? (Please let them be different from us.) These are complicated, compelling questions. But here, at the outer boundaries of the human condition, are realities that resist our understanding.

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In the public imagination, serial killers tend to fit a certain stereotype: “They’re all men, all white, all evil geniuses or mentally ill; they want to get caught,” Bonn said, listing the most prevalent myths. Even the serial killer exhibit at the Crime Museum claims, “Over 90 percent [of serial killers] are white males.”

In reality, Bonn says, “they are actually far more nuanced, far more varied than the general public realizes.” The racial breakdown of serial killers is about the same as that of the U.S. population at large, according to the FBI. Based on the Radford University serial killer database, which includes data on nearly 4,000 killers, just 46 percent of serial killers since 1910 have been white men.