PLANO, Tex. — From Day One of the Jan. 6 investigation, the FBI was after Person One — the Justice Department’s legal term for Elmer Stewart Rhodes III, a Yale-educated military veteran who founded the extremist group Oath Keepers.

He was not among the hundreds charged in the year after the attack with crimes ranging from assaulting a police officer to unlawfully entering the Capitol.

But he made frequent appearances in prosecutors’ court filings, which said that “Person One” was in regular contact with those who allegedly attacked Congress, pushing his disciples to prepare for an apocalyptic confrontation with those who would acknowledge Joe Biden’s presidential victory and the end of Donald Trump’s time in office.

On Thursday, a year and a week after the riot that rocked the U.S. Capitol, FBI agents in Texas arrested Rhodes, based on a newly unsealed indictment accusing him of the rare crime of seditious conspiracy.

He is the most high-profile person charged in the wide-ranging investigation to date.

Shackled at his wrists and ankles, Rhodes appeared briefly in federal court here Friday.

Magistrate Judge Kimberly C. Priest Johnson ordered him to remain in jail at least until a detention hearing on Jan. 20.

Wearing jeans, work boots and a green T-shirt, Rhodes, 56, seemed calm as he sat in the courtroom chatting with his attorneys, seated among other defendants in unrelated cases and surrounded by U.S. marshals.

Outside the courthouse, Rhodes’s lawyers, James Lee Bright and Philip Linder, told reporters that their client would seek to be released pending trial.

“He’s not a flight risk, he has no criminal history, no passport, and he’s not guilty,” Linder said.

Bright added that Rhodes “looks forward to fighting the charges.”

Another newly charged Oath Keeper, Edward Vallejo of Phoenix, appeared briefly before a federal magistrate judge in Arizona, who ordered that he, too, should be held in custody until a detention hearing next week.

Most seditious-conspiracy precedents are drawn from cases in the late 1700s or the early 1900s. The last time the Justice Department filed such charges was during the Obama administration, against self-styled militia members, and a judge rejected the case.

The last successful federal sedition prosecution came 26 years ago, when Omar Abdel Rahman, also known as the “blind sheikh,” and nine others were convicted of plotting to blow up the United Nations, the FBI building in Manhattan, and bridges and tunnels between New Jersey and New York.

“This will be a novel case in every way, since the precedent is extremely limited, but I think it’s an appropriate charge here,” said Ryan Fayhee, a former national security lawyer at the Justice Department who is now in private practice. “It takes a lot of care and courage to bring a case and use a statute that is very rarely used. . . . It will be one hell of a legal fight, no doubt about it.”

The law, which carries a maximum sentence of 20 years in prison, makes it a crime for people to “conspire to overthrow, put down, or to destroy by force the Government of the United States, or to levy war against them, or to oppose by force the authority thereof, or by force to prevent, hinder, or delay the execution of any law of the United States, or by force to seize, take, or possess any property of the United States contrary to the authority thereof.”

The way the law is written, it offers a potentially low bar to file a charge — in theory, simply delaying the execution of any law or taking any government property could result in charges.

But Fayhee argued that the nature of what Rhodes and his followers allegedly did before the Capitol was breached shows that Jan. 6 is the rare instance in which the spirit of the seditious conspiracy law can rightly be applied.

“What makes these defendants different is the alleged planning, the overt acts, the Capitol building, the communications and then the contradictions in the public record about the reason they were there,” said Fayhee.

Justice Department officials weighed possible sedition charges against some Oath Keepers for nearly a year, while legal experts publicly debated the potential pitfalls and advantages of using the law.

In late February or early March, according to a person familiar with the matter, prosecutors in the Washington U.S. attorney’s office prepared a memo outlining possible sedition cases that could be filed and sent it to the national security division at Justice Department headquarters.

Rhodes has denied any wrongdoing, saying he never entered the Capitol and never intended for members of his group to go in. Instead, he and other Oath Keepers have maintained that they came to Washington to safeguard high-profile individuals like Trump adviser Roger Stone during protests in support of the then-president’s false claims of widespread election fraud.

A day before his arrest, Rhodes ripped the FBI in an online interview with Northwest Liberty News.

“I have stuck my neck out and basically sacrificed myself, my own success, to do Oath Keepers. . . . I could be a wealthy lawyer if I had chosen that path, but I instead chose to sacrifice that and do the Patriot job,” Rhodes said, venting frustration that some on the extreme right have suggested he is an FBI informant.

“This is what the FBI does, they make you turn on each other, accuse each other and distrust each other,” Rhodes said. “It causes suspicion and distrust, even while they are manipulating people and groups.”

The 48-page indictment against Rhodes and 10 Oath Keeper adherents portrays him as the driving ideological force behind the group, drawing largely on the defendants’ own communications on encrypted messaging apps and other forums.

In one group message, on Dec. 11, 2020, Rhodes wrote that if Biden took office, “it will be a bloody and desperate fight. We are going to have a fight. That can’t be avoided.”

He made similar statements a day later at a pro-Trump rally in Washington.

On Christmas Day that year, Rhodes said in a secure chat with Florida Oath Keepers that he expected that Congress would probably certify Biden’s victory and that Trump’s “only chance . . . is if we scare the s--- out of them and convince them it will be torches and pitchforks time.”

The indictment says Rhodes bought weaponry in the days leading up to Jan. 6, spending about $15,500 in the new year on firearms and equipment including “a shotgun, scope, magazines, sights, optics, a bipod, a mount, a case of ammunition, and gun-cleaning supplies.”

In the two weeks between Jan. 6 and the inauguration, he allegedly spent an additional $17,500 on firearms, attachments and additional equipment.

The indictment charges that even after taking part in storming the halls of Congress, Rhodes’s followers were preparing to keep up their far-right rebellion.

“We got food for 30 days,” Vallejo allegedly said in a group chat on Signal, adding, “We have only [begun] to fight!”

On Jan. 11, another Oath Keeper, Jessica Watkins of Ohio, allegedly messaged a co-conspirator: “We’ve been organizing a bugout plan if the usurper is installed. . .Something like 20+ Oathkeepers going to Kentucky mountains on hundreds of acres apparently.” She suggested that they might adopt tactics of the North Vietnamese army during the Vietnam War by hiding out in tunnels.

Nevins reported from Plano. Barrett and Hsu reported from Washington.