MOUNT OLIVE, N.C. — The U.S. military trained him in explosives and battlefield tactics. Now the Iraq War veteran and enlisted National Guard member was calling for taking up arms against police and government officials in his own country.

Standing in the North Carolina woods, Chris Arthur warned about a coming civil war. Videos he posted publicly on YouTube bore titles such as “The End of America or the Next Revolutionary War.” In his telling, the U.S. was falling into chaos and there would be only one way to survive: kill or be killed.

Arthur was posting during a surge of far-right extremism in the years leading up to the Jan. 6 attack on the U.S. Capitol. He wrote warcraft training manuals to help others organize their own militias. And he offered sessions at his farm in Mount Olive, North Carolina, that taught how to kidnap and attack public officials, use snipers and explosives and design a “fatal funnel” booby trap to inflict mass casualties.

While he continued to post publicly, military and law enforcement ignored more than a dozen warnings phoned in by Arthur’s wife’s ex-husband about Arthur’s increasingly violent rhetoric and calls for the murder of police officers. This failure by the Guard, FBI and others to act allowed Arthur to continue to manufacture and store explosives around young children and train another extremist who would attack police officers in New York state and lead them on a wild, two-hour chase and gun battle.

Arthur isn’t an anomaly. He is among more than 480 people with a military background accused of ideologically driven extremist crimes from 2017 through 2023, including the more than 230 arrested in connection with the Jan. 6 insurrection.

At the same time, while the pace at which the overall population has been radicalizing increased in recent years, people with military backgrounds have been radicalizing at a faster rate. Their extremist plots were also more likely to involve weapons training or firearms than plots that didn’t include someone with a military background, according to an Associated Press analysis of domestic terrorism data obtained exclusively by the AP. This held true whether or not the plots were executed.

While the number of people involved remains small, the participation of active military and veterans gave extremist plots more potential for mass injury or death, according to data collected and analyzed by the National Consortium for the Study of Terrorism and Responses to Terrorism, or START, at the University of Maryland. START researchers found that more than 80% of extremists with military backgrounds identified with far-right, anti-government or white supremacist ideologies, with the rest split among far-left, jihadist or other motivations.

In the shadow of the Jan. 6 attack on the Capitol — led in part by veterans — and a closely contested presidential election, law enforcement officials have said the threat from domestic violent extremists is one of the most persistent and pressing terror threats to the United States. However, despite the increasing participation in extremist activity by those with military experience, there is still no force-wide system to track it. And the AP learned that Defense Department researchers developed a promising approach to detect and monitor extremism that the Pentagon has chosen not to use.

As part of its investigation, the AP vetted and added to the data and analyses provided by START, and collected thousands of pages of records and hours of audio and video recordings through public records requests.

Free of scrutiny in Mount Olive, Arthur stockpiled weapons, some with the serial numbers scratched off to make them untraceable. He trained a pack of Doberman pinschers as guard dogs. He rigged his old farmhouse, where he lived with his wife, their three kids and two children from her previous marriage, with improvised explosives, including a bomb hidden on the front porch and wired to a switch inside.

As early as 2017, his wife’s former husband had reported concerns about his children’s safety to military, federal and local authorities, according to call records and police reports. All the while, Arthur continued growing his business and connecting with more like-minded individuals.

In early 2020, a man with a raging hatred for police and an interest in building a militia in Virginia came to the farm, eager to learn.

A festering problem

Service members and veterans who radicalize make up a tiny fraction of a percentage point of the millions and millions who have honorably served their country.

However, when people with military backgrounds “radicalize, they tend to radicalize to the point of mass violence,” said START’s Michael Jensen, who leads the team that has spent years compiling and vetting the dataset.

His group found that among extremists “the No. 1 predictor of being classified as a mass casualty offender was having a U.S. military background — that outranked mental health problems, that outranked being a loner, that outranked having a previous criminal history or substance abuse issues.”

The data tracked individuals with military backgrounds, most of whom were veterans, involved in plans to kill, injure or inflict damage for political, social, economic or religious goals. While some violent plots in the data were unsuccessful, those that succeeded killed and hurt dozens of people. Since 2017, nearly 100 people have been killed or injured in these plots, nearly all in service of an anti-government, white supremacist or far-right agenda. Those numbers do not include any of the violence on Jan. 6, which left scores of police officers injured.

A month after people in tactical gear stormed up the U.S. Capitol steps in military-style stack formation on Jan. 6, the new defense secretary, Lloyd Austin, addressed the long-festering problem. He ordered a force-wide “stand down” to give time to local military commanders to discuss the issue with personnel. He empaneled the Countering Extremist Activity Working Group to study and recommend solutions. Among the group’s eventual recommendations was to clarify what was prohibited under the military’s ban on extremist activity. The revised policy, released in December 2021, now specifies that anti-government or anti-democratic actions are violations of the Uniform Code of Military Justice, federal laws that apply to all service members.

Some applauded the changes, but military and political leaders had been concerned about extremism in the ranks for years after a wakeup call in 1995 when Army veteran and white supremacist Timothy McVeigh killed 168 people in the Oklahoma City bombing. And the Pentagon, Department of Homeland Security and a research arm of the U.S. Justice Department have all funded START’s research.

Bishop Garrison, a U.S. Army veteran and former senior advisor to Austin, led the working group to address extremism following Jan. 6 and the widespread unrest in 2020 amid the COVID pandemic and a racial reckoning.

“We believe the vast majority of people who serve do so honorably, and this is a small group of individuals having an outsized impact,” Garrison told the AP. “But we also still need to analyze data to ensure that our hypothesis is correct and supported by fact.”

Yet a chief hurdle cited by Pentagon officials has been a lack of data — how to understand the scope of extremism in the ranks when there are millions of active-duty service members across all of the branches?

“What’s vexing about this is we don’t have a great sense of the scope of the problem,” then-Pentagon spokesman John Kirby told CNN in the weeks after Jan. 6. “Many of these people … work very hard to conceal their beliefs. We can’t be the thought police.”

The Pentagon did develop at least one way to detect extremist incidents across military branches and among civilian defense contractors. But it isn’t using it.

The method was revealed in a research memo published the summer after Jan. 6 that, until now, has not been released publicly. American Oversight, a nonpartisan watchdog group, obtained the memo through a Freedom of Information Act lawsuit it brought against the Pentagon and shared it with the AP.

In a project that began in September 2020 and lasted into 2021, DoD researchers studying “insider threats” and other security issues in the workforce developed a way to mine data from a DoD security clearance database to identify white supremacist and extremist incidents. This database included details from security incident reports filed about people who held security clearances — a wide swath of the military population, civilians and contractors included.

The operation identified hundreds of reported incidents of white supremacy and anti-government and other extremist activity over 20 years — the kinds of internal red flags that could identify issues with service members.

The researchers, whose names were redacted, wrote that the results were a first step toward developing a way to identify incidents of extremism, and that the method could be used in other DoD databases.

And while the research was shared among some departments in the DoD after Jan. 6, it never made it to Garrison, who was leading the Pentagon’s extremism working group, he told the AP. He called the oversight “problematic” given his, and the working group’s, mission.

“I am very surprised by the existence of the report.”

A defense official did not address why the report was not sent directly to the working group. In a statement, the official said the DoD is “committed to understanding the root causes of extremism and ensuring such behavior is promptly and appropriately addressed and reported to the proper authorities,” and that the department has enhanced its ability to track extremism allegations.

‘Very violent and very ugly’

Arthur’s young children sat atop a blue plastic tub on his farmhouse’s porch in Mount Olive, their feet dangling as their older sister tied their shoes. In the tub was an improvised bomb that Arthur had wired to a switch inside the house, according to evidence presented at Arthur’s trial.

“They would swing their feet as kids do and pop holes in it. I wasn’t very careful around (the explosives),” the older sister, the daughter of Arthur’s wife and her ex-husband, told the AP. The AP is not naming the children interviewed for this story because they are minors.

As an Army cavalry scout who served two tours in Iraq, Arthur learned more specialized skills than an average soldier, such as how to rig improvised explosives.