Five years ago today, a 22-year-old college dropout fatally stabbed three people at his apartment in Isla Vista, California, then shot 11 people near the campus of University of California, Santa Barbara, killing three of them, before shooting himself to death.

In an email manifesto he sent out before his rampage, and in YouTube videos discovered afterward, the gunman made his motivation clear: He was angry that he was still a virgin and that women preferred other men over him. “I don’t know why you girls aren’t attracted to me, but I will punish you all for it,” he said in his final video. The targets of his attack, he said, were “the very girls who represent everything I hate in the female gender: The hottest sorority of UCSB.”

The Isla Vista killer identified himself as an “incel,” or a member of an online community of “involuntary celibates” who are united in their hatred of the women who don’t want to have sex with them — and the men who are better at finding romantic partners. In extreme cases, incels’ resentment has curdled into violent extremism, and in a country like the United States, where guns are easily accessible, this violence has on occasion taken the form of a mass shooting.

“If somebody is going to be violent, they may use whatever they have available to be violent,” said Emily Rothman, a professor at Boston University School of Public Health and an expert on intimate partner violence. “And guns are far more lethal” than other weapons, she added.

Since his rampage, the Isla Vista gunman has been hailed as a “saint” and a hero by other incels, and several American mass shooters have cited him as inspiration. The 40-year-old self-proclaimed misogynist who shot six women, two of them fatally, at a Tallahassee yoga studio last year name-checked the Isla Vista gunman in one of his final online posts. The 21-year-old who fatally shot two students and himself at his former high school in Aztec, New Mexico, in 2017 used the Isla Vista shooter’s name as an online pseudonym and called him a “supreme gentleman.” The man who carried out the 2015 Umpqua Community College shooting in Oregon, which left nine people dead and eight others wounded, wrote in an online manifesto that he was a virgin with “no friends, no job, no girlfriend,” and said that he and others like him — including the Isla Vista gunman — “stand with the gods.”

Most recently, in January, a 27-year-old Colorado man was arrested after he posted online about wanting to become “the next mass shooter” and killing “as many girls as I see.” He cited his virginity and his persistent lack of a girlfriend as motivation.

Experts say these shooters crave attention and want to spread fear among those they feel have slighted them, and each incel shooting might inspire future acts of mass gun violence. “What happens in these communities is a kind of veneration of these figures who commit this violence,” said Arshy Mann, a Canadian journalist who has covered the incel phenomenon. “The more examples they have to look to the past, the more likely it is to happen.”

The Isla Vista rampage was the first time many people first encountered the term incel. But some incels reach back further than that for inspiration. In 2009, a computer programmer who wrote online that he hadn’t had a girlfriend in 25 years shot 12 women at an LA Fitness in Bridgeville, Pennsylvania, killing three of them, before killing himself. In fact, until Isla Vista, incels referred to such shootings as “going Sodini” — the LA Fitness gunman’s last name.

Last year, a self-described incel drove a van into a crowd in Toronto, killing 10 people and wounding 16 others. Prior to the attack, the perpetrator also sang the Isla Vista shooter’s praises online. One reason incel-perpetrated violence has not taken the form of mass shootings in Canada is that guns are not as widely accessible there.

Guns were key to the Isla Vista gunman’s transformation from online ranter to violent actor. “My first act of preparation was the purchase [of] my first handgun,” he wrote of his shooting spree, which he planned for 18 months. “After I picked up the handgun, I brought it back to my room and felt a new sense of power.”

There have also been many mass shooters who fit a similar profile, but who didn’t identify themselves as incels, including the Sandy Hook gunman; the Charleston church shooter; the Capital Gazette killer; the Santa Fe High School shooter, and the Parkland gunman. Others, like the Sutherland Springs and Pulse nightclub gunmen, had histories of domestic violence. Many mass shootings stem from domestic violence, and as The Trace has reported, a history of domestic violence is a risk factor that is often present in future mass shooters.

Some mass shooters who are motivated by misogyny are also driven by racism. Before the Charleston church shooter opened fire in 2015, killing nine people, he reportedly said to his black victims, “You rape our women and you’re taking over our country.” The Tallahassee yoga shooter said “whores” in interracial relationships had “betrayed their blood.” The notion that white women who date outside of their race are disloyal has been a running theme in parts of the incel online community. The overlap between the alt-right and incel communities is so significant that last year the Southern Poverty Law Center proclaimed the Isla Vista gunman to be the first alt-right killer.

Some experts say incel-inspired violence should be referred to as misogynist terrorism. Calling shooters “lone wolves” “ignores the preventable way these men’s fear and anger are deliberately cultivated and fed online,” feminist author Jessica Valenti wrote in The New York Times last year.

After the Isla Vista shooting, it came to light that police officers had visited the gunman’s home less than a month before the rampage at his mother’s request. They left without searching his apartment, but if they had, they would have found three semiautomatic handguns, ammunition, and the killer’s manifesto. As a result, California became the second state to institute a so-called red flag law, which allows for the disarming of someone deemed by a judge to be a threat to themselves or others. Since California, 13 other states have passed similar laws, and experts believe that they can be effective tools in reducing gun violence.

“In individual cases, these orders could make all the difference,” Garen Wintemute, the director of California’s publicly funded gun violence research center, told The Trace after the Parkland shooting. “The weapon matters. If there’s a high-risk situation, taking firearms out of the equation can change the outcome.”

Other experts say it’d be wise to deprive incels of the online platforms they use to disseminate their ideology. In 2017, Reddit banned the incel subreddit for inciting violence against women. They’ve since migrated to other sites, but Mann has urged a public pressure campaign when it comes to online communities where misogyny flourishes. “I think social media companies, online forums, and web hosting platforms need to think more carefully about the content that they allow on there,” he said. “And they need to understand the nuances of how these communities operate.”

In the long term, Rothman said, preventing violence against women must start in childhood. “We could be doing a heck of a lot more in terms of early intervention,” she said. “That means getting into elementary schools and identifying those who have displayed signs of aggression, or bullying — or being bullied — and linking them with behavioral health, a social and emotional learning curriculum, mentorship, coaching, and guidance. It’s a lot less expensive and a lot easier to catch people when they’re young and to try to help them than to wait until somebody is 30.”