While much remains unknown about the man who carried out an attack in New Orleans on New Year’s and another who died in an explosion in Las Vegas the same day, the violence highlights the increased role of people with military experience in ideologically driven attacks, especially those that seek mass casualties.

In New Orleans, Shamsud-Din Jabbar, a veteran of the U.S. Army, was killed by police after a deadly rampage in a pickup that left 14 others dead and injured dozens more. It’s being investigated as an act of terrorism inspired by the Islamic State group.

In Las Vegas, officials say Matthew Livelsberger, an active duty member of the U.S. Army Special Forces, shot himself in the head in a Tesla Cybertruck packed with firework mortars and camp fuel canisters, shortly before it exploded outside the entrance of the Trump International Hotel, injuring seven people. On Friday, investigators said Livelsberger wrote that the explosion was meant to serve as a “wakeup call” and that the country was “terminally ill and headed toward collapse.”

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. But an Associated Press investigation published last year found that radicalization among both veterans and active duty service members was on the rise and that hundreds of people with military backgrounds had been arrested for extremist crimes since 2017. The AP found that extremist plots they were involved in during that period had killed or injured nearly 100 people.

The AP also found multiple issues with the Pentagon’s efforts to address extremism in the ranks, including that there is still no force-wide system to track it, and that a cornerstone report on the issue contained old data, misleading analyses and ignored evidence of the problem.

Since 2017, both veterans and active duty service members radicalized at a faster rate than people without military backgrounds, according to data from terrorism researchers at the National Consortium for the Study of Terrorism and Responses to Terrorism, or START, at the University of Maryland. Less than 1% of the adult population is currently serving in the U.S. military, but active duty military members make up a disproportionate 3.2% of the extremist cases START researchers found between 2017 and 2022.

While the number of people with military backgrounds involved in violent extremist plots 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 AP and START.

More than 480 people with a military background were accused of ideologically driven extremist crimes from 2017 through 2023, including the more than 230 arrested in connection with the Jan. 6, 2021, insurrection — 18% of those arrested for the attack as of late last year, according to START. 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.

The AP’s analysis found that plots involving people with military backgrounds were more likely to involve mass casualties, weapons training or firearms than plots that didn’t include someone with a military background. This held true whether or not the plots were carried out.

Kristofer Goldsmith, an Army veteran and CEO of Task Force Butler Institute, which trains veterans to research and counter extremism, said the problem of violent extremism in the military cuts across ideological lines. Still, he said, while the Biden administration tried to put in place efforts to address it, Republicans in Congress opposed them for political reasons.

“They threw, you know, every roadblock that they could in saying that all veterans are being called extremists by the Biden administration,” Goldsmith said. “And now we’re in a situation where we’re four years behind where we could have been.”