SAN DIEGO - Calling itself "the Darkest Reaches of the Internet," the online forum that appears to have shaped the ideology of the accused Poway synagogue shooter is a notorious echo chamber of hate.

Here, violent uprisings are high-fived and body counts are referred to as "scores."

Anti-Semitic conspiracy theories are preached at length, and the role of Nazi symbolism in the white nationalist cause is a frequent topic of debate.

It's a place where bigoted views are not only nurtured, but propelled into violent action.

It all appears to have made a big impression on 19-year-old John T. Earnest.

A year and a half after tapping into the online community, a manifesto attributed to the Rancho Penasquitos resident appeared on the website, shortly before authorities say he opened fire on worshippers at the Chabad of Poway. A 60-year-old woman was killed in last weekend's attack, and wounded were the synagogue's founding rabbi, an 8-year-old girl and her uncle.

The forum, called 8chan, and others like it are increasingly serving as incubators for radicalization in the extremist alt-right movement.

Unlike the traditional Ku Klux Klan or skinhead gangs, these online communities lack hierarchy, organization and face-to-face connections that have bonded acolytes in the past. The forums have instead created loosely affiliated networks of like-minded people who can easily and anonymously engage from the privacy of their homes.

It's an evolution of hate that experts say hasn't seemed to receive the same attention or urgency as international terrorism, until recently.

The day before the attack in Poway, FBI Director Christopher Wray emphasized the "steady, persistent threat" domestic terrorism poses to the U.S.

"These folks aren't targeting the obvious - you know, the airport, the power plant," Wray said during an address to the Council on Foreign Relations. "They're targeting schools, sidewalks, landmarks, concerts, shopping malls with anything they can get their hands on, and sometimes things they can get their hands on pretty easily: knives, guns, primitive IEDs, cars."

The online forum allegedly frequented by Earnest was launched in 2013 but gained a significant following starting in 2014.

That's when a similar but tamer platform, 4chan, shut down all threads relating to a controversy known as Gamergate, a harassment campaign that targeted women working in the video game industry. So Gamergate proponents were encouraged to migrate to 8chan, where its operators strived for true freedom of expression.

Its only rule is against posting content that violates "the Digital Millennium Copyright Act or other United States law."

Robert Evans, an American investigative reporter for the United Kingdom-based website Bellingcat, has watched the forum evolve over the past few years into a place where hate speech now flourishes.

The forum caught his attention in 2016 during the presidential election, when Donald Trump tweeted an image of Hillary Clinton imposed over a background of money with a red, six-pointed star calling her "the most corrupt candidate ever." The meme was traced back to 8chan.

"They had a lot of success pushing memes through the mainstream," Evans said of the forum's participants, "and I wanted to monitor that."

What Evans found was hate speech that was once cloaked in sarcasm growing more explicit.

"The message board turned from a kind of ironic Nazism to just Nazism," he said. "There's still sort of a tongue-in-cheek aspect - but they're not joking."

Before the April 27 attack on the Poway synagogue, a post attributed to Earnest appeared on 8chan implying impending violence, with links to a long manifesto as well as a Facebook page where the shooting was apparently supposed to have been livestreamed.

"I've only been lurking a year and a half, yet what I've learned here is priceless," the anonymous poster declared.

The first commenter encouraged him to "get the high score."

Someone who saw the posting warned the FBI just moments before the shooting, but the agency could not act fast enough to prevent it because time and place were unknown.

The "open letter" attributed to Earnest contains the usual list of anti-Semitic grievances that white nationalists use to support their cause.

It is also a blatant call for others to follow his lead.

The letter writer said it was a similar manifesto penned by the suspect in the New Zealand mosque shootings in March that inspired him to act. Since the attacks - 51 dead at two mosques - the letter has been translated into many languages and widely circulated on social media.

"People who make these 'press kits,' what they are trying to do is use violence to provoke attention to a set of ideas they think will be contagious," said Joan Donovan, who leads research on the intersection of hate and technology at the Shorenstein Center on Media, Politics and Public Policy at Harvard Kennedy School. "They think it will catch on if enough people hear them and will mobilize."

Right-wing extremism in the U.S. appears to be rising, experts say.

The Transnational Threats Project for the Center for Strategic and International Studies, a policy research organization based in Washington, D.C., analyzed acts of terrorism by alt-right groups using the Global Terrorism Database.

Researchers found that between 2007 and 2011, the number of attacks was five or less a year. Attacks rose to 14 in 2012, and continued at a similar level for the next four years. In 2017, the number jumped to 31.

"What we're seeing now is a generational shift, because this broader movement has been around literally 200 years," Feshami said. "It goes through waves. The skinheads in the '80s, '90s, 2000s, those guys are aging out. They're still active and around, but not the center of the movement now. Now millennials are stepping in and adapting to the internet age."

Extremists in large part fight with weapons of propaganda, presenting a greater challenge to law enforcement who must constantly weigh constitutionally-protected speech against actual threats.

Their language "is all coded and it's all intended to skirt right up to the line," said Brette Steele, who has worked for federal law enforcement combating violent extremism and is the current director of prevention and national security at the McCain Institute for International Leadership.

The FBI is the federal law enforcement agency tasked with investigating terrorism threats, but agents are not constantly monitoring the activity on forums such as 8chan.

"We don't investigate a group or specific person unless we have probable cause to believe there's a violation of federal law," said FBI Assistant Special Agent in Charge Al Araiza, who leads the Joint Terrorism Task Force in San Diego. "We can't do it without a predicated offense because of the First Amendment. It's all protected speech."

"When it becomes an implied or specific threat," Araiza said. "Location, time, references to something in the past done. That gives us probable cause."

But by that time, even with warning, law enforcement often has limited time to react, as in the case of the Poway shooting, Araiza said.

There is no federal law specifically tailored for domestic terrorism, unlike international terrorism.

So domestic terror cases often are charged under a panoply of other federal and state crimes, from hate crimes to specific offenses such as murder, arson, bombing, firearm possession by a felon and criminal threats.

Of the approximately 5,000 terrorism cases the FBI currently has open, roughly 900 are domestic threats with no known international nexus, according to the agency.

But over the past two years, arrests in domestic terrorism cases have outnumbered international terrorism arrests, the FBI reports. In fiscal 2018, the FBI arrested about 120 domestic terrorism suspects compared to about 100 international. The year before it was 150 domestic versus 110 international.

Non-profits, journalists and private sector companies have been monitoring these online forums for several years.

Flashpoint, a for-profit company that helps clients in a variety of industries combat various threats, has developed techniques to track trends and escalations that might signal coming violence.

Other groups, like the non-profit Unicorn Riot, monitor and publish information found in far-right online communities.

In his address the day before the Poway shooting, FBI Director Wray acknowledged law enforcement can't combat extremism alone.

"We need to focus even more on a whole-of-society approach because in many ways we confront whole-of-society threats," he said. "It is very clear to me that the next few years will be very much defined by what kind of progress we can make with private-public partnerships."

Last Thursday, Facebook took a major step in banning a number of controversial figures associated with the far right, including Alex Jones of InfoWars and Milo Yiannopoulos. Actor James Woods also had his Twitter account suspended for a post that the company said violated its rules.

President Donald Trump reacted to the moves on Twitter: "I am continuing to monitor the censorship of AMERICAN CITIZENS on social media platforms. This is the United States of America - and we have what's known as FREEDOM OF SPEECH! We are monitoring and watching, closely!!"

Crafting clear, concise policies can be tricky.

"What type of content you do not want on your service and how you define that and enforce that is a really complicated challenge," said David Sullivan, director of learning and development with the Global Network Initiative, "and it's made more complicated when you have coordinated networks of ill-intentioned individuals and organizations who are trying to exploit loopholes and game the system."