The U.S. Army said that Jacob Fracker — one of the two off-duty Virginia police officers who have been arrested on federal charges related to the Capitol riot — is a corporal in the Virginia National Guard.
Fracker is the first known active military service member charged in the assault on the halls of Congress.
The disclosure of Fracker's status as a guardsman comes as thousands of National Guard service members, some of them armed, provide security in and around the Capitol in the wake of the deadly riot Jan. 6.
President Donald Trump was impeached Wednesday for inciting the mob, which objected to the election of Joe Biden as president.
Fracker and fellow Rocky Mount, Virginia, Police Officer Thomas Robertson were seen posing for a photograph, making obscene gestures, in front of a statue in the Capitol during the invasion, according to charging documents filed in U.S. District Court in Washington, D.C.
Other rioters that same day killed Capitol Police Officer Brian Sicknick, and beat and bear-sprayed other cops who defended the complex.
Four other people died during the melee, including an Air Force veteran, Ashli Babbitt, a rioter who was shot by police as she tried to climb through a blockaded area in the House of Representatives building.
Another member of the mob, retired Air Force Lt. Col. Larry Rendall Brock Jr., has been charged in the riot, where he was photographed on the Senate floor wearing a helmet and carrying zip-tie handcuffs.
Brock was carrying the handcuffs because he meant to "take hostages" and possibly "execute members of the U.S. government," a federal prosecutor told a judge, who allowed Brock to be released into home confinement in Texas on Thursday.
In a social media post that referred to the photo of him and Robertson, Fracker wrote, "Lol to anyone who's possibly concerned about the picture of me going around," according to the U.S. Attorney's Office for the District of Columbia, which is prosecuting both cops.
"Sorry I hate freedom?" Fracker wrote. "Not like I did anything illegal ... y'all do what you feel you need to."
Robertson, in his own taunting social media post after the attack, wrote, "CNN and the Left are just mad because we actually attacked the government who is the problem and not some random small business."
"The right IN ONE DAY took the f***** U.S. Capitol. Keep poking us," Robertson wrote, according to prosecutors. In an Instagram post, Robertson wrote that he was "proud" of the photo because he was "willing to put skin in the game."
Both Fracker and Robertson are each charged with a single count of knowingly entering or remaining in any restricted building or grounds without lawful authority, one count of violent entry and disorderly conduct on Capitol grounds.
They are each free on a $15,000 unsecured release bond and are barred from either going to Washington or taking part in any demonstration or protest as their criminal case continues.
Robertson told WSLS-10 News that the photo of him and Fracker was taken "long after any disorder and we were let in and escorted by Capitol Police."
He also said that, "I walked through an open door guarded by two Capitol police officers, was handed a bottle of water by then and asked to stay within a roped area, which we did."
Dozens of other people have been charged in the riot, which began after Trump held a rally on the Ellipse, where he urged supporters to march to the Capitol and help him fight to undo Biden's election as president.
In a statement to CNBC, the National Guard said, "Jacob Fracker is a corporal in the Virginia National Guard, and he serves as an 11B infantryman in a traditional National Guard status where he normally drills one weekend a month and two weeks of annual training."
"He is not currently on duty with Virginia National Guard troops in Washington, D.C." the spokesman said. "The Virginia National Guard will conduct an investigation into the matter, and we will be able to release more information when that is complete."
In its own statement, the Rocky Mount Police Department said it "takes this matter very seriously" and is investigating the incident.
In the meantime, Fracker and Robertson are on administrative leave pending that review, the police department said.
"The recent events that have taken place at our U.S. Capitol are tragic. We stand with and add our support to those who have denounced the violence and illegal activity that took place that day," the department said.
In a statement Tuesday, the Army had said it is working with the FBI to determine whether any participants in last week's riot have any connection to the Army.
"Any type of activity that involves violence, civil disobedience, or a breach of peace may be punishable under the Uniform Code of Military Justice or under state or federal law," an Army spokesperson wrote in an emailed statement to CNBC.
Gary Reed, director for intelligence at the Pentagon, in a statement Wednesday wrote, "We in the Department of Defense are doing everything we can to eliminate extremism in the Department of Defense."
"DoD policy expressly prohibits military personnel from actively advocating supremacist, extremist, or criminal gang doctrine, ideology or causes," Reed wrote.