The FBI investigation of the Capitol riot has begun to zero in on potential key figures in the chaos, including some self-styled militia members who in some videos and photos appear to be planning or urging further violence.

Though no one has been charged with leading or directing the violence, investigators are working to find out whether certain individuals helped coordinate aspects of the attack, before and during the chaos, or were merely opportunistic instigators.

In nearly two weeks since the assault, the Justice Department has charged more than 100 people — mostly individuals who revealed themselves as participating in the Jan. 6 riot through social media boasts. But the weekend arrests of people with alleged ties to extremist groups reflects the FBI’s increasing attention to the more prepared, organized and determined groups among the larger mass of rioters.

Some of the flags seen during the Jan. 6 Capitol siege symbolize support for far-right causes, white supremacy and anti-government militias. (The Washington Post)

One of those newly charged was Robert Gieswein, 24, of Woodland Park, Colo. Charging documents and videos indicate he may have links to the three extremist groups that have drawn the most attention from the FBI: the Proud Boys, Oath Keepers and Three Percenters. Some of the videos appear to include members who discussed storming the Capitol about an hour ahead of the riot.

In court papers, FBI agents say Gieswein — charged with assaulting police, civil disorder and obstruction of police and government — runs a private paramilitary training group and is affiliated with the Three Percenters. The FBI said in court filings that Gieswein was apparently recorded multiple times inside and outside the Capitol on Jan. 6, decked out in military garb with two distinctive markings that made it easier for investigators to trace his actions that day — a patch for his paramilitary group, the Woodland Wild Dogs, and a black pouch on his chest that said, “MY MOM THINKS I’M SPECIAL,” evocative of the Proud Boys anthem, “Proud of Your Boy.”

Someone who appears to match the description of Gieswein laid out in FBI arrest affidavits shows up on a live-streamed Proud Boys video from about 11:14 a.m. to 12:55 p.m. that day. About 30 minutes into the video, viewed by The Washington Post, one member in the group with people in blaze-orange hats, camouflage backpacks and military-style vests yells, “Let’s take the f---ing Capitol!” Someone else then admonishes, “Let’s not ­f---ing yell that.”

The group in the video waits at the Capitol until 12:48 p.m. to link up with milling supporters of President Trump who have made their way to the west front of the Capitol after the president’s speech at the Ellipse, the live stream shows. Once there, the Proud Boys group surges forward, toppling barricades and charging up the steps, with a Proud Boys narrator saying, “We’re storming the Capitol!”

Then, about 2:13 p.m., according to FBI affidavits, Gieswein appears in a different video with a helmeted group breaking a window on the Senate side of the Capitol using a riot shield and a piece of lumber, one of the earliest breaches of the building.

Gieswein turned himself in to authorities Monday and was in custody in Colorado. Information about his attorney was not available. Efforts to reach Gieswein and relatives, including people associated with his addresses and inoperative Web domains he registered in 2019, such as rockymountainoathkeepers.com and woodlandwilddogs.com, were unsuccessful.

The charges filed against Gieswein on Saturday do not include accusations that he conspired with others to attack Congress. But investigators are still working to better understand his role and interactions with others on the day of the attack and in the run-up to the violence, according to people familiar with the case who spoke on the condition of anonymity because the investigation is ongoing.

Before the attack, Gieswein gave a media interview in which he echoed anti-Semitic conspiracy theories, the affidavit said, and said his message to Congress was “that they need to get the corrupt politicians out of office. Pelosi, the Clintons . . . every single one of them, Biden, Kamala.”

On Monday, prosecutors unsealed charges against a Texas man associated with the Three Percenters who allegedly threatened to kill his children if they exposed him and a Pennsylvania 29-year-old accused of attacking police with a metal barricade.

Others also charged in recent days include a heavy-metal guitarist from Indiana and two self-styled militia members from Ohio — further signs that the FBI is ratcheting up its investigation of the role extremist organizations played in storming the building.

Jon Schaffer, who founded the band Iced Earth, turned himself in to FBI agents in Indianapolis on Sunday afternoon, officials said. On Jan. 6, Schaffer was photographed inside the Capitol, wearing a hat that said “Oath Keepers Lifetime Member.”

Schaffer was charged with six crimes, including engaging in an act of physical violence. Authorities said Schaffer was among the rioters who targeted Capitol Police with bear spray. At a pro-Trump march in November attended by Oath Keepers, the FBI said, Schaffer said: “We’re not going to merge into some globalist, communist system. It will not happen. There will be a lot of bloodshed if it comes down to that, trust me.”

Also arrested Sunday were Donovan Crowl, 50, a former Marine interviewed by the New Yorker, and Army veteran Jessica Watkins, 38. A bartender, Watkins recently told the Ohio Capital Journal that she formed the “Ohio State Regular Militia” in 2019 — a unit of the Oath Keepers, the FBI said — and that the group has appeared at a dozen rallies to “protect people.”

The FBI said Watkins posted to Parler a photograph of herself in uniform on Jan. 6, writing: “Me before forcing entry into the Capitol Building. #stopthesteal #stormthecapitol #oathkeepers #ohiomilitia.”

Watkins and Crowl were among about 10 people recorded at the Capitol wearing combat helmets, ballistic goggles, tactical vests and Oath Keepers patches who were shown to “move in an organized and practiced fashion and force their way to the front of the crowd” outside the Capitol, FBI affidavits said.

Attorneys for Crowl, Watkins and Schaffer could not immediately be identified.

The Oath Keepers, the Three Percenters and the Proud Boys, a male-chauvinist group with ties to white nationalism, have drawn particular attention from FBI agents investigating the attack on Congress as they work to determine whether those groups organized or directed the violence to block certification of President-elect Joe Biden’s election victory. Officials have said the Proud Boys in particular are an important focus of the FBI investigation.

“All these extremist groups are being looked at in terms of their participation at the Capitol,” Michael Sherwin, acting U.S. attorney for the District of Columbia, said Friday.

Oath Keepers patches and logos were prominently worn by a number of those in the mob that day. It is one of the largest self-described militia groups in the United States, claiming tens of thousands of members who assert the right to defy what they deem “illegal” government orders.

The Oath Keepers gained a measure of notoriety last summer when members showed up at Black Lives Matter protests wearing military gear and carrying weapons as a kind of self-declared vigilante force to prevent vandalism. Before that, they appeared at the 2014 standoff at the Bundy ranch in Nevada and the protests in Ferguson, Mo.

A related group, the Three Percenters, formed in 2008 and is named after the bogus claim that only 3 percent of the population fought against the British in the American Revolution. The self-described militia group espouses right-wing libertarian ideals and has embraced Trump. The group also has provided security services for various right-wing protests and movements, the FBI said.

Overall, many of those charged by the Justice Department have been what one senior law enforcement official characterized as “low-hanging fruit” — people who revealed themselves as participating in the riot on Jan. 6.

Federal investigators are now accelerating efforts to determine whether the assault was planned and led by groups of people — rather than an impulsive outburst of violence — particularly because some of the men shown on video laying siege to the building were equipped with handheld radios and headsets and at times appeared to work in unison on particular objectives, investigators said.

“There are breadcrumbs of organization in terms of what maybe was taking place outside the Capitol . . . with perhaps some type of communication with core groups of people ingressing into the Capitol,” Sherwin said, but he cautioned it could be weeks or months before the FBI settles on an answer “to find out the actual motivations of some of those groups.”

Even before the riot, the Oath Keepers had garnered attention and alarmed law enforcement officials. Stewart Rhodes, a former Army paratrooper who founded the group in 2009, threatened ahead of November’s election to deploy members to polling places, preemptively accusing Democrats of voter fraud on Alex Jones’s online show “Infowars.”

Members also demonstrated in Washington after the election in support of Trump. Rhodes, who has predicted the nation will descend into civil war, said allies would not recognize Biden’s victory as legitimate, adding in an interview with news outlet the Independent, “We’ll end up nullifying and resisting.”

Before the riot, law enforcement agencies were also increasingly concerned about the Proud Boys. The group’s chairman, Enrique Tarrio, had planned to attend Trump’s Jan. 6 rally but was arrested when he arrived in D.C. and charged with misdemeanor destruction of property in connection with the burning of a Black Lives Matter banner taken from a Black church during an earlier protest in Washington. He is also accused of felony possession of two extended gun magazines.

Tarrio told The Post last week that his group did not organize the Capitol siege.

“If they think we were organizing going into the Capitol, they’re going to be sadly mistaken,” he said. “Our plan was to stay together as a group and just enjoy the day. We weren’t going to do a night march, anything like that. That’s it as far as our day.”

In the Proud Boys’ Jan. 6 live-stream video, marchers refer to Tarrio and some address him via the stream. One leader taunts police by bullhorn, shouting before the riot, “You took our boy in, and you let our stabber go,” apparently referring to Tarrio’s arrest and a man allegedly involved in stabbing several Proud Boys in a December march on D.C.

U.S. authorities on Friday arrested Dominic Pezzola, 43, of Rochester, N.Y., a former Marine and Proud Boys member known as“Spaz” or Spazzo” who is allegedly visible helping Gieswein climb through the riot-shield-shattered Capitol window and confronting police with him inside the building. In court papers, the FBI cited a witness who told them that the group Pezzola was with would have killed “anyone they got their hands on,” including House Speaker Nancy Pelosi (D-Calif.) and Vice President Pence.

Since the attack, Proud Boys leaders have urged members to pull out of pro-Trump protests planned around Biden’s inauguration Wednesday.

Tarrio said he is actively discouraging members from attending planned armed marches. The Proud Boys, he said, are on a “rally freeze and will not be organizing any events for the next month or so.”

Jennifer Jenkins, Dalton Bennett and Julie Tate contributed to this report.