Jon Schaffer, a heavy metal guitarist and self-described "lifetime member" of the Oath Keepers, on Friday became the first Capitol rioter to plead guilty to charges based on his participation in the attack and has entered into a cooperation agreement with the government.

The move from Schaffer came at an unannounced proceeding before U.S. District Court Judge Amit Mehta on Friday morning. During a lengthy plea dialogue with Metha, Schaffer acknowledged that the deal requires him to "cooperate fully with the United States," from sitting for interviews to providing any evidence he has of known crimes. As part of the agreement, the Justice Department has offered to sponsor Schaffer for the witness protection program, Mehta noted.

Schaffer, who was seen on camera deploying chemical spray at officers, pleaded guilty to charges that he obstructed Congress’ effort to certify the 2020 election results and that he unlawfully entered a restricted building.

The plea negotiations with prosecutors and Schaffer were inadvertently disclosed earlier this month, when a sealed Justice Department filing was accidentally posted on the public docket. “The government’s ongoing plea negotiations with this defendant are the first and most advanced plea negotiations involving any of the over 300 Capitol Riot defendants,” prosecutors wrote in the April 5 filing.

The implication of Schaffer’s plea are not immediately clear. Prosecutors have charged a dozen members of the Oath Keepers with conspiring to stop Congress’ certification of the 2020 election on Jan. 6. But there’s been little public evidence of Schaffer’s connection to those defendants so far.

The Oath Keepers case, though, is among the highest-profile to emerge from the Capitol assault, when thousands of Donald Trump supporters descended on the Capitol, overwhelming — and in many cases assaulting — police officers. Hundreds of pro-Trump rioters breached the building, sending lawmakers and then-Vice President Mike Pence fleeing for safety.

Several of the Oath Keepers were part of a security detail that guarded longtime Donald Trump associate Roger Stone, who has denied any knowledge of the group’s incursion on the Capitol. The government has also produced hundreds of private messages the Oath Keepers exchanged discussing their plans for attending Trump’s Jan. 6 "Stop the Steal" rally and to provide security to certain attendees. Prosecutors contend their messages suggest the group was preparing for violence that day, and they’ve continued to reveal evidence that the Oath Keepers amassed a stockpile of firearms in the Virginia suburbs ahead of the Capitol incursion.

Attorneys for the Oath Keepers say the messages prosecutors have produced don’t include any reference to storming the Capitol. Rather, the attorneys argue, the Oath Keepers intended to guard against potential violence from anti-Trump counterprotestors like Antifa.

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