A Tampa man pleaded guilty Tuesday to joining a “stack formation” of Oath Keepers members and associates who allegedly breached the Capitol on Jan. 6, becoming the latest to cooperate with prosecutors and the first among the formation to specify that he intended to hinder Congress that day using intimidation and coercion.

Caleb Berry, 20, pleaded guilty to one count of conspiracy and one count of obstructing an official proceeding.

In a plea deal, prosecutors agreed to request lowering an estimated prison term of 51 to 63 months under federal guidelines for Berry, who has no criminal record and is one of the youngest defendants charged in the Capitol riots, in exchange for his substantial assistance.

U.S. District Judge Amit P. Mehta of Washington accepted the plea after Berry acknowledged that he coordinated plans and discussed the need to bring firearms for Jan. 6 in the nation’s capital with Oath Keepers members.

“Do you agree you intended to affect the government by stopping or delaying the congressional proceeding and in fact did so?” Mehta said, reading from a five-page statement. “You accomplished this by intimidating and coercing government personnel who were participating in or supporting the congressional proceeding?”

“Yes, your honor,” said Berry, who was released pending a court date in 60 days.

In plea papers, Berry admitted driving to Washington from Florida with other co-conspirators, meeting them the morning of Jan. 6 at a rally for President Donald Trump at the White House Ellipse and marching to the Capitol. They later walked single-file up the Capitol steps in camouflage, body armor and tactical gear and forced entry through the East Rotunda doors about 2:40 p.m., Berry admitted.

At least two other Oath Keepers associates — Graydon P. Young, 55, of Florida, who also admitted being part of the “stack,” and Mark Grods, 54, of Mobile, Ala., who said he entered minutes later — have also pleaded guilty and agreed to testify against others, describing encrypted communications and efforts to bring and store firearms at a hotel in nearby Arlington, Va.

Berry’s plea lacked such details, but all three men admitted that they and co-conspirators believed they were trying to obstruct a joint session of Congress meeting to confirm the 2020 election results.

Young and Grods in plea papers entered June 23 and 30, respectively, agreed that they acted to impede the congressional proceeding, without specifying their intent.

Berry attorney Daniel J. Fernandez of Tampa did not immediately respond to a request for comment.

Lawyers tracking the investigation said Berry and Young might now give prosecutors two “insiders” who can potentially identify and testify against others. They could also potentially describe the group’s possible purpose, planning and actions.

The timing of Berry’s plea — he was charged July 9 under seal — could also be calculated to step up pressure on remaining defendants. Seven U.S. prosecutors entered appearances in Berry’s case, from offices including the U.S. attorney’s office in Washington and the Justice Department’s national security division.

U.S. prosecutors have now charged all but one of 14 people associated with the “stack” or just trailing behind them, including Berry and Young, according to an online group of Internet sleuths calling itself Capitol Terrorists Exposers that has provided information to journalists and investigators that prosecutors have cited in court filings.

Prosecutors have charged 16 Oath Keepers associates in a single indictment. The group includes Young and other alleged organizers: Ohio bar owner Jessica Watkins, founder of a group billing itself as a militia; Navy intelligence veteran Thomas Caldwell of Virginia; and Florida auto-dealer executive Kelly Meggs.

All the others have pleaded not guilty to conspiring to impede Congress’s electoral-vote certification. Some have said they were in Washington to provide security for Republican VIPs including Roger Stone, or to support Trump in case he invoked the Insurrection Act and mobilized a citizen militia to pursue his unfounded claim that the election was stolen.

Assistant U.S. Attorney Kathryn C. Rakoczy said in court earlier this month that “many if not most” of the 16 were in “productive” plea talks.

Prosecutors have now charged more than 20 associates of the group in the riot, alleging that 16 conspired through GoToMeeting planning calls and encrypted messaging apps about their plans in Washington, including staging weapons in advance at an Arlington hotel for a “Quick Reaction Force.”