Retired military servicemen are turning up in alarming numbers on wanted posters and in charging documents as federal agents continue their sweep of arrests tied to the deadly riot at the Capitol last week, a trend that has experts increasingly concerned about the dangerous allure of extremist and paramilitary groups.

So far at least nine of those arrested for participating in the riot have been confirmed to be former members of the U.S. military, ABC News has confirmed through court files, lawyer statements, and military records.

The actual number is likely higher. On Thursday, FBI Director Chris Wray said the bureau has made over 100 arrests in connection with the riot, with many more anticipated.

“The large number of individuals with ties to law enforcement or the military already arrested or apparently now under investigation suggests a deeper level of far-right sympathizers in these fields,” said Javed Ali, a former senior director for counterterrorism at the National Security Council.

Some experts have been sounding alarm bells about the issue for years.

Among the ex-military arrested following last week’s attack was Larry Rendell Brock, who invaded the Capitol alongside Eric Gavelek Munchel, with both of them sporting military uniforms and gear, including zip ties, according to the Department of Justice. Munchel, of Tennessee, and Brock, of Texas, were among the first arrests as FBI agents sought to determine whether they could have been engaged in a plot to take lawmakers hostage.

The Air Force confirmed to ABC News that Lt. Col. Brock retired in 2014 after more than two decades of service, noting he had served as an A-10 pilot until 2007.

Brock was released to home confinement on Thursday, according to the Associated Press. In an interview with The New Yorker, Brock said, “The president asked for his supporters to be there to attend, and I felt like it was important, because of how much I love this country, to actually be there.” He has not yet entered a plea.

Other arrested individuals include David Lester Ross, a former member of the Massachusetts National Guard, who was taken into custody on Jan. 6 near the Capitol building after he “did not obey at least three warnings” from officers to disperse, according to arrest records. Ross pleaded not guilty at his arraignment on Thursday, and was released and ordered to stay away from D.C. His lawyer, Darry Daniels, declined to comment when reached by ABC News.

On Friday, ABC News confirmed the man seen on video smashing through the window of the Capitol building with a police shield is a former Marine. The man, Dominic Pezzola, was in the Marines for seven years as an infantry assault man, the Marine Corps told ABC News. He had won a National Defense Service Medal.

Pezzola was taken into custody Friday morning, according to the FBI, who said he is the same person seen in images “smoking a cigar inside the Capitol building.”

Earlier this week, the FBI questioned a former reserve Navy SEAL after he boasted in a Facebook video about “breaching the Capitol.” The video shows Adam Newbold, 45, from Lisbon, Ohio, whom the Navy confirmed is a retired reserve SEAL special warfare operator, in a car on his return home from Washington, telling his Facebook followers that he had wanted to make lawmakers “think twice about what they’re doing” and leave them “shaking in their shoes.”

When reached by ABC News on Tuesday, Newbold pleaded for forgiveness for his participation, saying: “I am not a terrorist. I am not a traitor.”

In the oath they take upon enlisting, U.S. military personnel and officers swear to “support and defend the Constitution of the United States against all enemies, foreign and domestic.”

Mary McCord, a longtime national security expert who now runs Georgetown Law’s Institute for Constitutional Advocacy and Protection, told ABC News that the radicalization of military servicemen and their participation in the Capitol riot last week isn’t surprising to her and has long been an issue.

“Some unlawful militias specifically recruit from the military because of their expertise in firearms, explosives, and tactical skills,” McCord explained. “And the idea of continuing to have a mission can be very appealing to ex-military, especially if they are predisposed ideologically with the unlawful militias.”

McCord called it “a serious problem” and said it’s something that the military “should be addressing” — both with respect to active duty and former military members.

Calls for discipline against former military members who participated in the riot have been growing since last week.

“I think we should throw the book at them, to the furthest extent possible,” said Rep. Ruben Gallego, D-Ariz. “If you’re off active duty, I want to figure out a way we can bring you back and charge you.”

“And if you’re convicted, we should be able to take your benefits away,” Gallego added.

Military personnel who retire after 20 years of service are entitled to benefits like monthly military retirement pay, access to Department of Defense medical care and health plans, and access to military commissaries. Those who leave prior to 20 years of service get no military retirement pay or access to DOD military care, but do have access to Veterans Affairs benefits like health care and home loans.

On Monday, Sen. Tammy Duckworth, D-Ill., sent a letter to acting Defense Secretary Chris Miller requesting that the Defense Department’s criminal investigative organizations work with the FBI and Capitol Police to investigate current and retired military members who may have participated in the attack. In the letter she urged Miller “to take appropriate action to hold individuals accountable under the Uniform Code of Military Justice.”

“Upholding good order and discipline demands that the U.S. Armed Forces root out extremists that infiltrate the military and threaten our national security,” wrote Duckworth.

In court, though, ex-servicemen have been citing their military backgrounds in seeking special consideration from the court — or pardons from President Donald Trump.

“My client fought — was in the military, served honorably. No criminal background whatsoever,” said the attorney for Jacob Chansley, also known as Jake Angeli, the man who was photographed during the riot wearing horns and body paint. “And he, like a lot of other disenfranchised people in our country, felt very, very, very solidly in sync with President Trump.”

ABC News has confirmed that Chansley used to be a Navy supply clerk.

And Virginia police officers Thomas Robertson and Jacob Fracker appear to have posted a photo of themselves with their middle fingers raised, in front of the statue of John Stark in the Capitol, according to the Department of Justice’s statement of facts in the case. After the riot, Robertson repeatedly defended his participation, saying he was “proud” of the photo because he “was willing to put skin in the game,” according to the DOJ document.

The two officers have been put on administrative leave, according to a statement from the town of Rocky Mount, where they both work. During an interview with a local media outlet, Robertson said he and Fracker “did not participate in any violence or property damage,” and suggested that Capitol Police allowed them into the building.

The Army confirmed to ABC News that Fracker is a current corporal in the Virginia National Guard, though they emphasized that he is not on duty with the Virginia National Guard troops currently in D.C.

“The Army is committed to working closely with the FBI as they identify people who participated in the violent attack on the Capitol to determine if the individuals have any connection to the Army,” they said in a statement.

Appearing before a federal judge following his arrest, Robertson cited what he described as 23 years of military experience as the reason he should not be detained pending trial.

The judge agreed and ordered Robertson released on bond.

ABC News’ Luis Martinez, Ben Siegel and Luke Barr contributed to this report.