Two Proud Boys members have been arrested after they stormed the Capitol two weeks ago, including a leader of the extremist right-wing movement, Joseph Biggs.
They were both among crowds that besieged the country’s legislature on 6 January with baseless claims that November’s election was “stolen” from Donald Trump, who departed the White House on Wednesday when Joe Biden was sworn in as president.
Congress had been working to certify the Democrat’s election win when the attack took place.
Mr Biggs was described as being an organiser for the Proud Boys by the FBI, and was charged with disorderly conduct, obstructing an official, and entering a restricted area at the US Capitol on the day of the attack.
He appeared in court in Orlando shortly after his arrest on Wednesday, and was released under home confinement and other restrictions, according to CNN and court documents.
The Justice Department and an FBI affidavit said Mr Biggs had been identified through digital media as being part of a crowd that overcame Capitol Police who were manning a metal barrier on the steps of the Capitol.
He was among the first to break into the building, having walked through a door opened by rioters who had broken a small window with a police body shield, NBC News reported.
Mr Biggs admitted to FBI agents on Monday that he had entered the Capitol building, but denied breaking in with force. He also denied having any knowledge about the planning of the attack and did not know who organised it, the affidavit said.
The FBI said some Proud Boys members were seen wearing earpieces during the attack, while Mr Biggs appeared to be wearing a walkie-talkie, the affidavit said.
And in posts to social media, Mr Biggs told other Proud Boys members on the alternative right-wing platform Parler that they should dress in black to disguise themselves, while also resembling far-left antifa activists, according to the affidavit.
Mr Rivera also faces charges of entering a restricted building, intent to impede US government business, disorderly conduct and demonstrating at the Capitol. He was said to have shared a video on Facebook showing himself in the US Capitol crypt during the attack.
The Proud Boys, an extremist all-male group known for engaging in violent clashes at political rallies, were told by Mr Trump in September to "stand back and stand by" during a presidential debate with Mr Biden, when asked to denounce their actions.
They were among hundreds who besieged Congress on 6 January alongside other extremist groups and conspiracy theorists. The events left five people, including a Capitol Police officer, dead.
The FBI have since arrested more than a 100 individuals who took part in the riot, while some 200 are said to be under investigation.
Additional reporting by Associated Press