A founding member of the right-wing Oath Keepers militia group on Friday became the first person to plead guilty to taking part in the US Capitol riot, signalling a new stage in the investigation of the deadly January 6 assault on the seat of American democracy.

Jon Schaffer, a native of Indiana and founder of the band Iced Earth, entered a guilty plea to two felony charges of obstructing the certification of the 2020 election and breaching a restricted building.

Iced Earth’s singer and bassist quit the band in February.

During a hearing in Washington, DC federal court, US District Judge Amit Mehta said Schaffer, 53, had no previous criminal record and voluntarily contacted authorities shortly after the Capitol riot.

Protesters supporting US President Donald Trump gather near the Senate chamber of the US Capitol after groups breached the building’s security on January 06, 2021 [File: Win McNamee/Getty Images/AFP]
The judge indicated that Schaffer was involved in discussions about cooperating with government investigators and agreed to release him from custody on his own recognisance, with another hearing scheduled for mid-June.

Schaffer is among hundreds of supporters of former President Donald Trump who stormed the Capitol in an attempt to overturn the November election results. Rioters battled with police, smashed windows and sent lawmakers fleeing for safety.

Five people, including Capitol Police officer Brian Sicknick, died in the violence.

Prosecutors said Schaffer wore a tactical vest and carried bear spray repellent when he joined the attack on the Capitol 100 days ago.

A lawyer for Schaffer agreed at Friday’s hearing that Schaffer entered the Capitol that day as Congress prepared to certify the Electoral College vote in favour of Joe Biden.

In a court filing, prosecutors said Schaffer, who was photographed during the Capitol riot wearing a cap with the insignia of the right-wing Oath Keepers, “was among the rioters who sprayed United States Capitol Police officers with ‘bear spray'”.

The Oath Keepers have been linked to others in Trump’s orbit, including Roger Stone, a longtime supporter and friend of the former president.

Members of the Oath Keepers provide security to Roger Stone at a rally the night before groups attacked the US Capitol, in Washington, DC, on January 5, 2021 [File: Jim Urquhart/Reuters]
Prosecutors said Schaffer was “photographed and captured on surveillance video” carrying the bear spray and also was filmed “engaging in verbal altercations with Capitol Police officers inside the Capitol Building”.

More than 400 people have been arrested and charged with taking part in the violence. The most serious charges have been assault, conspiracy and obstruction of Congress or law enforcement.