In 2014, Jerad and Amanda Miller walked into a Las Vegas pizza restaurant and shot and killed two local police officers on their lunch break. Then the married couple fatally shot a shopper before dying during a shootout with responding officers. Credit: Facebook.com

Leaderless resistance isn’t a new phenomenon. Last year, the Southern Poverty Law Center published a comprehensive study on domestic terrorism between 2009 and 2015 and found that 74 percent of the attacks were carried out by a person acting alone, without any outside money or direction.

Like Omar Mateen.

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Information still is emerging on the man who walked into Pulse, a gay nightclub in Orlando, Florida, in the early hours of June 12, killing 49 people and wounding dozens of others. But Mark Potok, senior fellow at the Montgomery, Alabama-based Southern Poverty Law Center, who helped author the “Lone Wolf Report,” said Mateen seems to fit the profile of a lone wolf.

“What does not look likely is that he had any real support from overseas,” Potok said. “It does not seem to have been remotely like the 9/11 attackers, who really were sent to this country as part of a major plot that was devised elsewhere.”

Now, officials also are looking into Mateen’s wife – investigating whether she knew about his plans. Potok said that when lone wolves aren’t acting alone, they’re typically tight-knit pairs: a father and son, a wife and husband. If you include these small groups, about 90 percent of the attacks the law center looked at could be considered “lone wolf” attacks.

In 2014, Jerad and Amanda Miller walked into a Las Vegas pizza restaurant and shot and killed two local police officers on their lunch break. Then the married couple fatally shot a shopper before dying during a shootout with responding officers.Credit: Facebook.com Credit: Facebook.com

Jerad and Amanda Miller, a married couple from Indiana, moved to Las Vegas in January 2014. Six months later, according to the report, they walked into a pizza restaurant there and shot and killed two police officers on their lunch break – Igor Soldo, 31, and his partner Alyn Beck, 41. They left a swastika and a Gadsden flag on one of the officer’s bodies – the flag is a symbol used by the anti-government patriot movement.

The couple then headed to a nearby Walmart and fatally shot a shopper, Joseph Wilcox, 31. The Millers died during a shootout with responding officers.

By operating alone or in small groups, lone-wolf terrorists often fly below law enforcement’s radar because they typically aren’t very social and are unlikely to tell anyone their plans, which makes it pretty much impossible for someone to step in and stop them.

Lone wolves are especially hard to recognize if they haven’t had prior contact with law enforcement.

“That was obviously the case with Dylann Roof, who really had no history at all of political violence,” Potok said, referring to the man who has been charged with the murder of nine people in a Charleston, South Carolina, church last year.

Dylann Roof, who has been charged with the murder of nine people in a Charleston, South Carolina, church last year, didn’t have any contact with a hate group or white supremacists before the attack. Credit: Centralized Bond Hearing Court via AP Credit: Centralized Bond Hearing Court via AP

Potok describes Roof as a “classic example of the modern lone wolf.” He never had any direct contact with any hate group, and he never met with other white supremacists. He simply trolled around the internet looking at websites.

“One day, (he) typed the words ‘black on white crime’ into Google and came upon a racist webpage run by a group called the Council of Conservative Citizens that catalogued alleged black-on-white crime,” Potok said.  “And based on that, Roof decided to act – to actually go out and start killing people.”

The Southern Poverty Law Center found that about 51 percent of the attacks it examined were motivated by hate. This is a category that includes people who are inspired by racism, homophobia and radical Islam. But the rest were motivated by the antigovernment “patriot movement,” a broad group of right-wing – and mostly white – Americans that the FBI considers domestic terrorists.

Most of the cases may have received little news coverage or may have been reported as terrorist attacks. Many of them were committed by white Americans not influenced by foreign terrorist groups, but they are included because they had political motivations, according to the law center’s analysis.

There are even a few cases in which the perpetrator was not identified or caught. They’re listed as “unknown.”

The Southern Poverty Law Center used data by Indiana State University and the University of Maryland to identify domestic terrorist attacks from April 1, 2009, to Feb. 1, 2015. It cast a wide net and included cases that might’ve involved mental illness or personal grudges but had “an obvious political aspect.” The report covered both terror attacks that were actualized and those that officials were able to stop.

The timeline below shows every domestic terrorist the law center named in its report.

Julia B. Chan worked at The Center for Investigative Reporting until June, 2017. Julia B. Chan is a producer and the digital editor for Reveal's national public radio program. She’s the voice of Reveal online and manages the production and curation of digital story assets that are sent to more than 200 stations across the country. Previously, Chan helped The Center for Investigative Reporting launch YouTube’s first investigative news channel, The I Files, and led engagement strategies – online and off – for multimedia projects. She oversaw communications, worked to better connect CIR’s work with a bigger audience and developed creative content and collaborations to garner conversation and impact.

Before joining CIR, Chan worked as a Web editor and reporter at the San Francisco Examiner. She managed the newspaper’s digital strategy and orchestrated its first foray into social media and online engagement. A rare San Francisco native, she studied broadcasting at San Francisco State University, focusing on audio production and recording. Chan is based in Reveal's Emeryville, California, office.

Scott Pham is the news applications developer for Reveal. Previously, he was the digital editor for the NBC Bay Area Investigative Team. Before that, he worked at numerous places in the public radio system, reporting for broadcast and innovating online. At KBIA public radio in Columbia, Missouri, he led the station to a national Murrow Award for best website and founded the Missouri Drone Journalism Program, which produced some of the very first drone-enabled journalism in the U.S. Pham is based in Reveal’s Emeryville, California, office.