As members of the Oath Keepers paramilitary group shouldered their way through the mob and up the steps to the U.S. Capitol, their plans for Jan. 6 were clear, authorities say. “Arrest this assembly, we have probable cause for acts of treason, election fraud,” someone commanded over an encrypted messaging app some extremists used to communicate during the siege.

A little while earlier, Proud Boys carrying two-way radios and wearing earpieces spread out and tried to blend in with the crowd as they invaded the Capitol led by a man assigned “war powers” to oversee the group’s attack, prosecutors say.

These two extremist groups that traveled to Washington along with thousands of other Trump supporters weren’t whipped into an impulsive frenzy by President Donald Trump that day, officials say. They’d been laying attack plans. And their internal communications and other evidence emerging in court papers and in hearings show how authorities are trying to build a case that small cells hidden within the masses mounted an organized, military-style assault on the heart of American democracy.

“This was not simply a march. This was an incredible attack on our institutions of government,” Assistant U.S. Attorney Jason McCullough said during a recent hearing.

The Proud Boys and the Oath Keepers make up a fraction of the more than 300 Trump supporters charged so far in the siege that led to Trump’s second impeachment and resulted in the deaths of five people, including a police officer. But several of their leaders, members and associates have become the central targets of the Justice Department’s sprawling investigation.

It could mean more serious criminal charges for some rioters. On the other hand, mounting evidence of advance planning could also fuel Trump’s and his supporters’ claims that the Republican former president did not incite the riot and therefore should not be liable for it.

Defense attorneys have accused prosecutors of distorting their clients’ words and actions to falsely portray the attack as a premeditated, orchestrated insurrection instead of a spontaneous outpouring of election-fueled rage to stop Congress’ certification of Trump’s defeat by Democrat Joe Biden.

And prosecutors’ case against a man described as a leader in the Proud Boys’ attack took a hit last week when a judge ordered him released while he awaits trial, calling some of the evidence against him “weak to say the least.”

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The Oath Keepers began readying for violence as early as last November, authorities say. Communications show the group discussing logistics, weapons and training, including “2 days of wargames.”

“I need you fighting fit” by the inauguration, one Ohio member, Jessica Watkins, told a recruit in November, according to court documents. “If Biden becomes president our way of life as we know it is over. Our Republic would be over. Then it is our duty as Americans to fight, kill and die for our rights,” she said in another message later that month.

As Jan. 6 neared, they discussed stationing a “quick reaction force” outside Washington that could bring in weapons “if something goes to hell,” according to court documents. Days before the attack, one man suggested getting a boat to ferry “heavy weapons” across the Potomac River into their “waiting arms.”

“I believe we will have to get violent to stop this,” that man, Thomas Caldwell of Virginia, said in a November message to Watkins. On Jan. 1, he took to Facebook to decry what he viewed as a rigged election, saying “we must smite them now and drive them down,” authorities say.

Authorities have acknowledged there’s no evidence Caldwell was a dues-paying member of the Oath Keepers but have described him as a supporter who appeared to play a “leadership role” within the group.

There were plans for some Oath Keepers to be there in “grey man” mode without identifiable militia gear so they could blend in with the crowd.

“For every Oath Keeper you see, there are at least two you don’t see,” said a Jan. 4 email sent to members.

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Two days before the attack, the Proud Boys’ top leader, Enrique Tarrio, was arrested shortly after he arrived in Washington and was charged with vandalizing a Black Lives Matter banner at a historic Black church during a December protest.

Tarrio was ordered to stay away from the nation’s capital, so Ethan Nordean was given “war powers” to take charge of the group’s Jan. 6 activities, prosecutors say.

Nordean, a Proud Boys chapter president from Washington state known as Ruffio Panman, tapped his social media following to solicit donations of money and tactical gear for the rally, prosecutors said. On the day of Tarrio’s arrest, Nordean posted a link to a podcast in which he discussed baseless claims about fraud in the election.

“Democracy is dead? Well, then no peace for you. No democracy, no peace,” he said.

Publicly, Tarrio announced on social media that the Proud Boys wouldn’t be wearing their customary yellow-and-black polo shirts on Jan. 6 so they could be “incognito.” Joseph Biggs, a self-described Proud Boys organizer from Florida, echoed that in a social media post directed at counter-protesters.

“We will be blending in as one of you. You won’t see us,” Biggs wrote. “We are going to smell like you, move like you, and look like you.”

Privately, according to prosecutors, the Proud Boys arranged for members to communicate using specific frequencies on Baofeng radios, Chinese-made devices that can be programmed for use on hundreds of frequencies, making it difficult for outsiders to eavesdrop.

One of the Proud Boys who heeded the call to meet in Washington was Dominic Pezzola. He traveled from Syracuse, New York, on Jan. 5 and stayed with other members at a hotel, authorities say.

Another group of members came from the Kansas City area. Investigators believe their chapter leader, William Chrestman, brought a helmet, a gas mask and an ax handle that he would conceal as a flag.

They were ready for a fight, prosecutors say.

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Long before the riot, Trump refused to condemn the Proud Boys during his Sept. 29 presidential debate against Biden, instead saying the group should “stand back and stand by.” Proud Boys members celebrated his words on social media, before the president later claimed not to know who they were. It’s unclear whether the Oath Keepers were on the White House radar.

Proud Boys members, who describe themselves as a politically incorrect men’s club for “Western chauvinists,” have frequently engaged in street fights with antifascist activists at rallies and protests. Vice Media co-founder Gavin McInnes, who founded the Proud Boys in 2016, sued the Southern Poverty Law Center for labeling it as a hate group.

The Oath Keepers are a loosely organized group of extremists who actively recruit current and former military, police and first responders who pledge to fulfill the oath to defend the Constitution against all enemies — foreign or domestic.

In the weeks before the attack, Trump and his supporters were making increasingly false and incendiary comments, designed to mobilize supporters to work to overturn the election results — even though there was no widespread fraud in the election, as was confirmed by election officials across the country and by Trump’s attorney general.

Trump encouraged thousands at the rally preceding the riot to “fight like hell,” but lawyers for the former president adamantly denied during his impeachment trial that he had incited the attack. They pointed to a remark during his speech in which he told the crowd to behave “peacefully” that day.

He was acquitted in a Senate trial of inciting the riot after he was impeached by the House, but GOP leaders said a more appropriate venue for his actions could be the courts.

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As the mob swarmed the Capitol, Stewart Rhodes, the leader of the Oath Keepers, was communicating with some of the alleged rioters.

“All I see Trump doing is complaining. I see no intent by him to do anything. So the patriots are taking it into their own hands. They’ve had enough,” he said in a Signal message to a group around 1:40 p.m., authorities say. A little later, Rhodes, who has not been charged in the attack, instructed the group to “come to South Side of Capitol on steps.”

Around 2:40 p.m., members of a military-style “stack” who moved up Capitol stairs in a line entered the building through a door on the east side, authorities say. Lawmakers and Vice President Mike Pence had been evacuated from the House and Senate chambers just about 20 minutes earlier.

“We are in the mezzanine. We are in the main dome right now. We are rocking it. They are throwing grenades, they are fricking shooting people with paint balls. But we are in here,” Watkins declared over a channel called Stop the Steal J6 on the walkie-talkie app Zello.

“Get it, Jess. … Everything we (expletive) trained for,” someone responded, according to the communications obtained by WNYC’s “On the Media” program and detailed in court documents.

Caldwell, who did not join the stack, climbed up to the west side balcony, authorities say.

“We are surging forward, doors breached,” he said in a Facebook message about 10 minutes after the group went inside, according to court documents. Roughly 15 minutes later he sent another message: “Inside.”

Caldwell received a Facebook message saying “all members are in the tunnels under capital seal them in,” authorities said. “Turn on gas,” the message said.

Hours after the siege, Caldwell was already talking about another attack “at the local level,” authorities say.

“If we’d had guns I guarantee we would have killed 100 politicians. They ran off and were spirited away through their underground tunnels like the rats they were,” Caldwell said in a message to a friend.

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The Proud Boys met at the Washington Monument and were already at the Capitol before Trump finished addressing thousands of supporters near the White House. Listening to the president’s speech wasn’t part of their plan, prosecutors say.

Nordean led the way with a bullhorn while they wore headgear marked with orange tape. Pezzola appeared to have an earpiece in his right ear. Biggs had what looked like a walkie-talkie device on his chest.

Nordean was spotted having a brief exchange near the Capitol with Robert Gieswein, a bat-wielding Colorado man. Proud Boys planning for Jan. 6 had discussed using non-members, or “normies,” like Gieswein to “burn that city to ash” and “smash some pigs to dust,” prosecutors said.

The Proud Boys arrived at the east side of the Capitol before noon. Nordean allegedly positioned them at a Capitol grounds pedestrian entrance guarded by a handful of police officers behind a movable metal barrier.

Around 12:50 p.m., just before the joint session of Congress was scheduled to start, a crowd including Proud Boys members broke through a front line of Capitol police officers and past sets of metal barriers. Nordean moved to the front of the crowd and “stalked” the line of officers to intimidate them and rile up the crowd, prosecutors wrote.

As the mob advanced to another line of officers in the Capitol’s west plaza, Chrestman faced them and shouted, “Do you want your house back?”

“Yes!” the crowd replied.

“Take it!” Chrestman yelled.

Gieswein and Pezzola were among the first to enter the Capitol, through a window Pezzola shattered with a riot shield that he snatched from police, prosecutors say. It took Pezzola more than an hour to fight his way from the exterior of the Capitol grounds to the building’s interior, they say.

Inside, Pezzola joined others in confronting Capitol Police Officer Eugene Goodman, who led the mob away from an entrance to the Senate chamber. Pezzola later took a video of himself smoking a cigar.

“Victory smoke in the Capitol, boys,” he said.

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Nine people linked to the Oath Keepers have been indicted on charges that they planned and coordinated with one another in the siege. At least 11 leaders, members or associates of the Proud Boys charged in the riots are accused by the Justice Department of participating in a coordinated attack.

Several from both groups remain in federal custody while awaiting trial.

Their defense attorneys say prosecutors have painted a misleading account of the day’s events based on shaky evidence. Other lawyers for those charged with storming the Capitol have tried to pin the blame on Trump for inciting the rioters.

Nordean’s lawyers said prosecutors haven’t presented any evidence that he used encrypted communications to lead a group’s attack on the Capitol. While the government said investigators found a Baofeng radio in Nordean’s home, his lawyers said he did not obtain it until after the day after the riot.

“The government has made repeated claims about Ethan’s activities and then backed away from them without providing any support,” said one of his attorneys, Nicholas Smith.

Caldwell’s lawyer has accused prosecutors of twisting social media posts and messages to make fantastic claims with no hard evidence that any person or group had a premeditated plan to storm the Capitol. David Fischer described Caldwell as a Hollywood-addicted amateur screenwriter full of bravado. The prosecutors’ case is heavy on “dramatic language” but “light on specifics,” the lawyer said in a recent court filing.

“What time was the ‘invasion’ scheduled to begin? Who would lead the attack? What was the goal once the planners entered the Capitol? Who was the leader in the attack? What was the exit strategy of the planners?” Fischer wrote.

Fischer said prosecutors’ case crumbles when closely examined. The “quick reaction force” prosecutors have alleged the Oath Keepers were planning, for example, was actually one person — an obese man in his late 60s with a bad back — who planned to come to their aid if they were attacked by left-wing protesters, Fischer said.

During a hearing last month in which a judge ordered him to remain behind bars while he awaits trial, Caldwell exclaimed that his messages were being “taken out of context.”

“These Oath Keepers thought they — ” he said, before the audio was disconnected and the judge cut in to warn him that anything he said could be used against him by prosecutors.

Richer reported from Boston, and Kunzelman reported from College Park, Maryland.