"Ted Bundy was the first criminal I ever took a real interest in," says Nicole Jane, a 23-year-old film student from the United Kingdom. After Ted, she developed crushes on several other serial killers. "It's a turn-on hearing about how they killed and what they used."

After Nicole Jane took to the Internet to learn more about her feelings of attraction, she discovered that there's a term for her predilections: hybristophilia. According to Psychology Today, sexologist Professor John Money first defined hybristophilia as a paraphilia in which one "derives sexual arousal and pleasure from having a sexual partner who is known to have committed an outrage or crime, such as rape, murder, or armed robbery." It's also known as Bonnie and Clyde syndrome.

Read more: When Women Help Their Husbands Rape and Murder

"I've always been into hybristophilia, even before I knew what it was," says Cherry, an 18-year-old from Portland, who first learned about the fetish by reading confessions from other women attracted to serial killers on a now-dismantled Tumblr. She says that she gets turned on by the thought of her partner committing violence; she was very pleased, for instance, when she learned that her boyfriend had stabbed someone in the past.

Psychology bloggers have presented various theories for why someone would be attracted to a perpetrator of violence, including the desire to change a man, the tendency to see a wounded child inside the criminal, or—in the cases of groupies who fixate on famous serial killers—the hopes of getting in on the media spotlight.

"I started to research and found there had been very few studies about it. I did find that [psychologists] had decided hybristophiles fall into two categories: aggressive and passive," says Nicole Jane. Those with the passive form of this kink have no interest in participating in the violent crimes, whereas aggressive hybristophilia refers to those people who desire to be a part of the excitement. "If I had to choose, I'd choose passive, purely based on the fact I would never hurt someone unwillingly," she adds.

"So there's two parts to [hybristophilia]: There's that taboo danger part to it, and there's this hyper-masculine aggressive part that could be very appealing to some women," explains Dr. Michael Aaron, a NYC-based sex therapist and author of the upcoming book Modern Sexuality.

While this kink is typically applied to heterosexual women, men can experience it as well. "There are certainly men who are attracted to dangerous women, as they may also be attracted to the thrill and emotional intensity such women evoke. [There's] less information available, as there are very few female serial killers," says Aaron.

Tanya, a 23-year-old self-identified hybristophile from the UK, says she fantasizes about having sex with a criminal mastermind. "I have a particular weakness for any crime that requires intelligence and calculation," she tells Broadly. "This might include something like a robbery or a heist. This group leader would be researching, developing tactics, even using their personal skills to gather information."

"I'd be lying if I said murder wasn't on the list, although I recognize this as a terrible thought," she adds, somewhat sheepishly.

[Men who commit violent crimes] give in to the animal, uninhibited selves, and I love the rawness of that.

In essence, Tanya finds men who commit violent crimes sexy because they "have more balls than most ever will." "Someone like Charles Bronson—he is hot," she specifies. (Bronson, also known as Charles Salvador, has been called "the most violent prisoner in Britain," as the Guardian reported, and he frequently received nude photos from female admirers while in prison.)

"I imagine him as a pretty primal man, and that's a huge kicker for me: erasing the social standards and people being stripped of their polite, groomed ways," Tanya elaborates. "[Men who commit violent crimes] give in to the animal, uninhibited selves, and I love the rawness of that."

Nicole Jane wrote her dissertation on hybristophilia and how it's represented in film. She thinks that the fetish is an unattainable—or at least unrealistic—fantasy for most. "It's all a false fantasy; that's my view on hybristophiles," she says. "I feel like a majority of people who identify as a hybristophile want someone who is cruel but forget the simple fact [a cruel person can't] really care for you."

Along with Ted Bundy, Nicole Jane has a fascination with Paul Bernardo, a Canadian serial rapist who committed a series of sexual assaults and murders during the late eighties and early nineties—all with the help of his wife, Karla Homolka, an "aggressive" hybristophile, who even helped Bernando drug, rape, and kill her younger sister.

"Her providing a victim for him removes herself from the equation as a potential victim," muses Nicole Jane. "That mentality—that the guy who hurts other will never harm me—is insanely interesting. Delusional, but interesting, and probably one I'd share if I was truly unhinged."

Nicole Jane is currently dating a man who identifies as a sadist in the BDSM sense of the term. While she finds his sexual enjoyment of her pain arousing, she says she'd never want to be involved with someone who actually has the capacity to commit violence outside of a roleplaying scenario.

"Someone who is aroused by risky and seemingly dangerous things, such as serial killers, is also probably going to be more likely to be interested in other intense, risky, or 'dark' activities," says Aaron. "They are attracted to certain themes that play out in different ways."

A penchant for bondage certainly doesn't equate lust for serial rapists, but Nicole Jane is not alone in using BDSM scenes to act out dangerous fantasies. Cherry—whose boyfriend you may recall stabbed someone (in self-defense, she adds)—will "indulge me by running his knife on my skin and talking about slitting my throat," she says.

These women say acting out these fantasies in a consensual manner allows them to practice them without actually sleeping with someone truly evil. "I'd never put myself in danger of being a real victim," Cherry states firmly.

Nicole Jane agrees. "I think if I was to ever find someone who was deeply disturbed and had no empathy for human life, I'd be terrified," she says.

For some hybristophiles, however, a lack of empathy is beside the point—or, perhaps, the major draw. The women who sent naked pictures to Charles Bronson are not at all unique: There are several cases of women becoming infatuated with convicted serial killers and even starting relationships with them as they're serving time in prison. Carol Anne Boone, for instance, married Ted Bundy and had his child. Serial killer Richard Ramirez married magazine editor Doreen Lioy while in prison, and in 2014 news broke that Charles Manson had been granted a marriage license—although later reports allege that his 26-year-old bride to be only wanted him for his corpse, so she could keep him in a crypt and charge people money to come and ogle his body.

"It is very common, for real serial killers in general, in jail to get lots of fan mail. They get engaged, and they get married! A lot of them," says Dr. Aaron.