▶ Watch Video: The Oath Keepers militia group’s path to breaching the Capitol

A third alleged member of the Oath Keepers has agreed to plead guilty and cooperate with prosecutors investigating the January 6 Capitol riot, according to court documents unsealed Wednesday.

Mark Grods, who prosecutors said brought firearms to D.C. and was part of the tactical “stack” formation that advanced toward the Capitol that day, was expected to enter a guilty plea Wednesday afternoon, and his testimony could confirm many of the government’s allegations against the far-right group.

If a judge accepts his guilty plea, Grods would become the third Oath Keeper to cut a deal with prosecutors, who describe the group as a large but loosely organized collection of individuals, some of whom are associated with militias. The Oath Keepers are at the center of one of the highest profile conspiracy cases connected to the Capitol riot, with 16 alleged members indicted together in a single conspiracy case.

Grods was scheduled to plead guilty to two charges — criminal conspiracy and obstruction of an official proceeding — and prosecutors said his charges and plea negotiation were part of an ongoing grand jury investigation related to the 16-person case. They asked the courts to keep his charges under seal this week while he worked with the government and testified before the grand jury.

Charging documents in Grods’ case were filed in court Monday but unsealed Wednesday, and include allegations that place Grods at the center of multiple key claims in the 16-person case. Prosecutors say he brought firearms to Washington, D.C., rode with other Oath Keepers in golf carts and was part of the military-style “stack” formation that stormed the Capitol that day.

No alleged Oath Keepers have been charged with firearms violations. Prosecutors have alleged in multiple court filings that some in the group brought firearms, but were aware of D.C.’s strict gun laws and opted to stow them outside of the city January 6 — a system prosecutors said was designed to provide access to the weapons. Prosecutors say Grods brought his firearms to D.C. but gave them to another individual to store in a Virginia hotel, and his cooperation could add more weight to prosecutors’ claims.

Prosecutors also said Grods attended or scheduled trainings for paramilitary combat tactics, recruited others to support the January 6 operation and brought paramilitary supplies to D.C., including combat uniforms, tactical vests, helmets and radio equipment.

Grods was also part of a group, prosecutors said, who rode in a pair of golf carts towards the Capitol, “at times swerving around law enforcement vehicles,” before parking the carts and continuing on foot towards the building.

Grods moved with others in a military-style “stack” formation through a restricted area toward the building, prosecutors said, and entered the Rotunda while carrying a large stick. He left the building minutes later, as law enforcement deployed pepper balls, prosecutors said.

Prosecutors said that two days after the siege, another person told Grods to make sure “all signal comms about the op has been deleted and burned.” Grods told the person he had done so, prosecutors said.

When arguing that the case should be kept under seal until Wednesday morning, prosecutors said that disclosure of his case could reveal the scope and direction of their investigation. Prosecutors also wrote, “Disclosure of these documents and this docket would endanger other aspects of the government’s ongoing investigation, including the destruction of evidence and the safety of potential witnesses, to include the defendant.”