(CNN) An Oath Keeper who served as private security for right-wing figures around January 6 pleaded guilty to seditious conspiracy and is cooperating with the Justice Department, becoming the first person charged with seditious conspiracy related to the attack to strike a plea deal.
Joshua James, who led the Alabama chapter of the Oath Keepers, a far-right extremist group, also pleaded guilty to obstruction of an official proceeding. He faces up to nine years in prison and up to a $300,000 fine, according to the deal read aloud during Wednesday's hearing.
The development is a major step forward for prosecutors who brought the ambitious case, with some of the most serious charges in the January 6 investigation. Other Capitol riot defendants with ties to the Oath Keepers who did not face sedition charges have already agreed to cooperate.
James, a Purple Heart recipient in the military, was originally arrested in March of last year for his alleged participation in the riot.
During the hearing, James admitted that he and other members of the Oath Keepers had planned to storm the Capitol with the explicit goal of stopping the certification of the 2020 Electoral College vote.
"Do you agree that in taking such actions, you were trying to influence the conduct of the United States government or retaliate against the United States government?" federal Judge Amit Mehta asked during the hearing.
"Yes sir," James responded.
An FBI agent previously told the court that James had chauffeured Roger Stone, a longtime friend of former President Donald Trump, in a golf cart in Washington the day before January 6, 2021. Stone has not been accused of any crime.
According to his plea agreement, James met with Oath Keepers members, including founder Stewart Rhodes, in November 2020. During the meeting, James learned of "their plans to oppose by force the lawful transfer of presidential power," according to court documents.
The alleged plan required members of the Oath Keepers, at Rhodes' direction, to use "any means necessary" to stop Joe Biden from becoming president, including using lethal force if anyone tried to forcibly remove Trump from the White House.
In the indictment charging James and other Oath Keepers with seditious conspiracy, prosecutors alleged that members of the group had organized to disrupt Congress' certification of the 2020 election and to "oppose by force the lawful transfer of presidential power," stashing weapons and ammunition in a Virginia hotel as part of a quick reaction force and continuing to plot an attack after January 6.
The indictment also alleges that in the aftermath of the riot, while other Oath Keepers plotted whether to take future action, James messaged an associate, "After this ... if nothing happens ...its war ... Civil War 2.0."
On January 6, James rushed to join the riot in a golf cart. He and two other alleged Oath Keepers, Roberto Minuta and Jonathan Walden, entered the Capitol, at times brawling with police, according to the plea agreement.
After the riot, James admitted that he, Rhodes and other members of the Oath Keepers took precautions to conceal their identities, including changing their appearance and using burner phones.
James also admitted that he had gone on "multiple trips" with Rhodes to buy thousands of dollars' worth of firearms, ammunition and tactical gear.
This story has been updated with additional details.