Zach Rehl, the longtime leader of the Philadelphia Proud Boys, was indicted Monday along with four other leaders of the organization on seditious conspiracy charges tied to the storming of the U.S. Capitol last year — a significant escalation of the Justice Department’s allegations surrounding their role in fomenting the violent assault.

Rehl, 36, had already faced charges of conspiring to obstruct the certification of the 2020 presidential election.

The historically rare sedition charge lodged against him and his codefendants — including Enrique Tarrio, the Proud Boys former national chairman, two other regional leaders of the far-right group, and a member from the group’s New York chapter — is the most serious accusation prosecutors have brought against any of the more than 800 people charged with playing a role in the attack.

» READ MORE: 62 Pennsylvanians have been charged in the Capitol riot. A year later, judges are starting to weigh their punishments.

To date, the Justice Department has levied sedition charges in only one other case — a sprawling indictment against Stewart Rhodes, the founder and leader of the extremist group the Oath Keepers, and 10 other members of his organization.

Conviction requires prosecutors to prove that the men were seeking to either overthrow the government or interfere with the execution of federal law and carries a maximum sentence of up to 20 years in prison.

Rehl, a Marine veteran and son and grandson of Philadelphia police officers, has remained in custody without bail since his initial arrest in March 2021. He could not be reached for comment Monday.

His attorney, Carmen Hernandez, said her client “maintains his innocence more so now than before.”

“The latest charge — seditious conspiracy — requires use of force, and there is no allegation he did use force,” she said.

It remains unclear what new evidence prompted the additional charges, which came in the form of a 10-count superseding indictment unsealed Monday against Rehl; Tarrio; Proud Boys chapter presidents Ethan Nordean, of Washington, and Joseph Biggs, of Florida; and Dominic Pezzola, a Proud Boys member from New York.

Since the initial indictment last year, one Proud Boys lieutenant — Charles Donohue, of North Carolina, who was originally charged alongside Rehl and the other men — has pleaded guilty and is cooperating with the government’s investigation into the group.

Authorities have also searched the homes of three other Proud Boys members — including Aaron Whallon Wolkind, the vice president of the Philadelphia Proud Boys and Rehl’s top lieutenant — though they have not yet been publicly charged.

But those investigative steps and the new charges unsealed Monday demonstrate prosecutors’ efforts to capture a wider picture of cooperation and organization among the multiple extremist groups that played a role in Washington on Jan. 6, 2021.

For example, prosecutors have previously cited video evidence in Tarrio’s case of a meeting in an underground parking garage in the days leading up to the attack. Among the participants were Tarrio, Rhodes, and Joshua Macias — the leader of the right-wing, pro-Trump group Vets for Trump who was arrested in Philadelphia in November 2020 after he drove from Virginia in a Hummer filled with guns and ammunition in an alleged attempt to disrupt the election vote count underway at the city’s convention center.

In the new indictment, prosecutors described Rehl and the others as key forces in planning the assault on the Capitol building in the days before Jan. 6 and stirring up the crowd during the attack.

Hoping to avoid mistakes from past rallies that had devolved into open street brawls with far-left activists, the group decided to maintain a lower profile. They’d leave their traditional black-and-gold polo shirts at home, equip themselves with encrypted radios, and focus their attentions on riling up “normies” — or unaffiliated supporters of President Donald Trump — they could hide behind.

They encouraged members from across the country to descend on Washington that day, used websites to raise money for travel and equipment, outfitted members with paramilitary gear and tactical vests, and developed plans to avoid detection.,

A week before the attack, Tarrio, according to the indictment, was sent a nine-page document titled “1776 returns” setting forth a plan to occupy a few “crucial buildings” in Washington D.C. including the House and Senate chambers with as “many people as possible” to “show our politicians We the People are in charge.”

That same day, prosecutors say, Rehl warned the others on a video call that Jan. 6 was going to be a “completely different operation” for the group and that this time, the Proud Boys would be doing more than “flexing our [arms] and shit.”

One member of that group said on that Dec. 30 call that Rehl, who Tarrio had deputized along with Biggs and Nordean to lead the Proud Boys in Washington, spoke with the same authority as Tarrio himself.

Tarrio “is not going to tell you something different than Zach is going to tell you,” the unnamed leader said. “It’s all one operation plan.”

Though Tarrio was not in Washington on the day of the attack, prosecutors have said he “remained in contact with other members of the Proud Boys” during the storming of the Capitol building.

Video footage from that day shows Nordean, Biggs and Rehl — wearing a camouflage “Make America Great Again” cap and carrying a Temple Owls backpack — leading a crowd of roughly 100 Proud Boys members from the Washington Monument toward Capitol security lines.

There, rioters — including Pezzola — threw themselves into the fray brawling with police and smashing their way into the building.

» READ MORE: Prosecutors put Philly Proud Boys president Zach Rehl at heart of Jan. 6 planning in new Capitol riot filing

Photos later surfaced showing Rehl inside the building, smoking a cigarette amid a mob of rioters carousing in the office of Sen. Jeff Merkley (D., Ore.).

And as the chaos continued to unfold, prosecutors say, Tarrio posted a voice memo to an encrypted Proud Boys messaging group proudly stating: “Make no mistake … We did this …”

Later that night, Tarrio sent another message, referencing “The Winter Palace” — a nod to both the imperial palace in St. Petersburg, Russia that was stormed by the Bolsheviks during the Russian Revolution of 1917 as well as a section of the Proud Boys’ planning document that had been called “Storm the Winter Palace.”

Lawyers for Rehl, Tarrio, Nordean, Biggs, and Pezzola maintain that ‘the plan’ their clients were discussing was simply to rally in Washington in support of former President Donald Trump and that none of them arrived on Jan. 6 intent on committing violence or fomenting a riot.

Hernandez, Rehl’s attorney, said Monday that he plans to fight the new charges, as he had the original case.

» READ MORE: Three more Philadelphia Proud Boys have been charged in Capitol riot after taking photos inside a senator’s office

As of Monday afternoon, a crowdfunding account managed by “friends and family of Zach Rehl” on the Christian website GiveSendGo — popular among far-right extremist organizations — had raised more than $43,300 in contributions for his family.

The page, which features a photo of Rehl between two images of the U.S. Constitution, describes the Philadelphia Proud Boys’ leader as “a father, a husband, Marine Corps Veteran, and Patriot who loves his Country.”

Three additional members of the Proud Boys’ Philadelphia chapter — Isaiah Giddings, 29, of Philadelphia; Brian Healion, 31, of Upper Darby; and Freedom Vy, 36, of Philadelphia — have also been indicted on lesser charges tied to the riot. They were not named in the new indictment Monday against Rehl and his codefendants.