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Before allegedly killing 10 people with a van in Toronto, Alek Minassian appeared to have posted a message on Facebook that linked him to a toxic online community of misogynists that has become the source of a growing pattern of violence.

The Facebook post, which authorities who spoke with NBC News believe came from Minassian, links Minassian to an online community known as “incels,” short for involuntary celibates. The Canadian Broadcasting Corporation also reported that Facebook confirmed the authenticity of the post.

Self-described incels congregate mostly online, meeting in forums and message boards like Reddit and 4chan, and its offshoot site 8chan, to discuss their hopelessness with women in posts that are peppered with racist and misogynistic rants. “Chads” are incel-speak for good-looking men, who incels believe can’t be one of them. “Stacys” are the women who find “Chads” attractive.

The Facebook message also refers admiringly to Elliot Rodger, who killed six people in Isla Vista, California, in 2014, and left behind a manifesto and videos detailing his sexual frustration as the motivation for his violence.

Rodger has since emerged as a source of inspiration among the incel community.

“Private (Recruit) Minassian Infantry 00010, wishing to speak to Sgt 4chan please. C23249161. The Incel Rebellion has already begun! We will overthrow all the Chads and Stacys! All hail the Supreme Gentleman Elliot Rodger!” Minassian allegedly posted.

A courtroom sketch of Alek Minassian. John Mantha

Minassian’s post spread quickly among the incel community, many of whom rushed to embrace him.

“I hope this guy wrote a manifesto because he could be our next new saint,” one poster wrote on incel.me, a forum where incels congregate.

While some posters questioned whether Minassian, 25, was a “fakecel” — the term for someone whose average looks disqualifies him from community membership — most hailed him as a hero of the movement.

“Spread that name, speak of his sacrifice for our cause, worship him for he gave his life for our future,” one poster wrote.

Another poster wondered whether Minassian might have been acting on his own March call to action for incels to commit mass murder and serial rapes, a post on incels.me which has since been removed.

“I want to see some mass food poisoning deaths, maybe a pipe bomb or two, or hopefully somebody finally uses a f---ing truck to just ram down [women] during a school parade or something, mix it up a little,” wrote BlkPillPres, whose username is a nod to the black pill, lingo in the incel community for coming to the realization that a woman will never have sex with them.

Violence perpetrated by men connected to misogynistic online communities has become systemic enough to warrant attention from organizations that track hate groups. The Southern Poverty Law Center added misogynistic organizations to their list of hate groups for the first time this year.

Heidi Beirich, the director of the Southern Poverty Law Center’s Intelligence Project, said that the incel community mostly consists of aggrieved young men, who have found a natural home on 4chan and darker parts of Reddit.

“They’re young, frustrated white males in their late teens into their early twenties who are having a hard time adjusting to adulthood. They’re the same kinds of people you find in white supremacy writ large,” Beirich said. “They have grievances about the world they’ve placed onto women and black people.“

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In a news conference on Tuesday, Toronto Police Services Det. Sgt. Graham Gibson acknowledged that most of Minassian's victims were women.

"That's fair to say. Predominantly female," Gibson said of those injured and killed.

Beirich places much of the blame for the growth of hateful incel communities on web forums and social media platforms that don’t proactively enforce rules limiting hate speech. When asked by a Reddit user earlier this month whether “open racism, including slurs” were against the site’s rules, CEO Steve Huffman wrote in a comment on Reddit, “it’s not.”

“Reddit has basically just said, ‘We don’t care if there’s bad stuff in these hate forums.’ 4chan and 8chan are completely outside the bounds of normality,” Beirich said. “When millions can be exposed to heinous propaganda, you are setting the table for ultimately hate speech and ultimately hate crimes.”

Beirich called incels a subgroup of both the men’s rights activist and alt-right movements.

“You’d be shocked at the amount of violence, raping, killing and attacking of women they advocate,” Beirich said. “In the case of Elliot Rodger, there was violence on a mass scale.”

Reddit banned the channel r/incels in November, citing a violation of its “violent content” rules. The shutdown followed a number of posts where members seemed to be advocating for rape and specifically one cross post in the channel r/legaladvice where a frequent r/incels poster appeared to be soliciting tips for how to get away with rape.

Quickly, members of the community moved over to r/braincels, which called itself a “fun, energizing, and thought-provoking atmosphere for incel culture.”

The subreddit, or Reddit community, has been active for over six months, and highlights the difficulty that comes with a whack-a-mole style of enforcement that Reddit and other platforms use to ban extremist groups from their sites.

Reddit did not immediately respond to a request for comment.

A full day after the attack, a post titled “The post about the Toronto killer being an incel has been proven to be fake” remained pinned to the top of the subreddit, along with a post denouncing the attack.

The third top-rated post on r/Braincels at press time featured a cartoon of a mouse wearing a Nazi armband beneath an oven timer, titled “Hi, lurking journalists!”

Hours after Minassian’s rampage, Reddit banned “malecels” — a subreddit for incel discussion where “normies” and women were prohibited that was only live for 19 days.

In one of the final posts to malecels, a user bragged the community would “not be banned anytime soon. Even if we advocate rape.”

“The admins are only competent when they get reports and because we'll be very vigilant of letting outsiders in there's no way admins would ever know what's going in here,” the user wrote. “There are far too many private subreddits for an admin to reasonably monitor.”

Anne Marie D'Amico, 30, was among 10 people killed in Monday's attack. Tennis Canada via AP

Minassian’s visible online footprint is small. He was briefly active on the gaming forums Steam, and once released an app through the Android app store that showed users available parking spaces in Toronto.

This wouldn’t be the first time a mass murderer blamed involuntary celibacy for his crimes.

In 2009, before the internet gave incels a known place to congregate, George Sodini walked into an L.A. Fitness gym in Pittsburgh and shot up a women’s aerobics class, killing four, including himself. Sodini left behind a blog where he detailed his plans and complained of rejection from women.

“There are 30 million desirable women in the US (my estimate) and I cannot find one. Not one of them finds me attractive,” he wrote.

Rodger, who Minassian referenced by name in his Facebook post, listed sexual frustration and a hatred for women as his chief motivation for his killing spree.

In his posts, Rodger spoke in language common among the incel and pickup communities, separating men into groups of alphas and betas and reducing women to entitlements that could be won or stolen.

Rodger closed his manifesto with: “All I ever wanted was to love women, and in turn to be loved by them back. Their behavior towards me has only earned my hatred, and rightfully so! I am the true victim in all of this. I am the good guy.”

In 2015, Chris Harper-Mercer killed nine and injured seven at a community college in Roseburg, Oregon, before turning the gun on himself. In his journal, Harper wrote: “My whole life has been one lonely enterprise. One loss after another. And here I am, 26, with no friends, no job, no girlfriend, a virgin.”

In his writings, he identified with Rodger as well as other mass shooters, whom he described as “people who stand with the gods.”

In February Nikolas Cruz, 19, who shot and killed 17 students and teachers inside Marjory Stoneman Douglas High School in Parkland, Florida, praised Rodger in a Youtube comment.

“Elliot rodger will not be forgotten,” Cruz wrote.

CORRECTION (April 25, 2018, 2:25 a.m. ET): An earlier version of this article misstated the name of Canada's public broadcaster. It is the Canadian Broadcasting Corporation, not the Canadian Broadcasting Company.