Jon Schaffer, a member of the far-right militia group Oath Keepers, has pleaded guilty for his role in the Jan. 6 Capitol riots—making him the first defendant to do so.

The Associated Press reports Schaffer entered the plea deal Friday and has agreed to cooperate with the feds in their ongoing investigation into the deadly siege. The 53-year-old, who is also the frontman for the Iced Earth metal band, was allegedly spotted among the mob that entered the Capitol building on Jan. 6 in an apparent effort to stop the certification of Joe Biden’s presidential win. Schaffer turned himself into the FBI just 11 days after the attack and remained behind bars up until his plea.

He pleaded guilty to obstruction of an official proceeding as well as entering and remaining in a restricted building with a dangerous or deadly weapon. He faces up to 30 years in prison if convicted of the charges.

Federal investigators say Schaffer admitted to being one of the first rioters to enter the Capitol, donning a tactical vest and carrying a chemical irritant spray that’s typically used to ward off bears. 

“The defendant in this case admits forcing his way into the U.S. Capitol on January 6 for the express purpose of stopping or delaying congressional proceedings essential to our democratic process,” FBI Deputy Director Paul M. Abbate said in a statement. “The FBI and our partners will continue to utilize all available authorities to aggressively investigate, pursue and hold accountable those who committed acts of violence or otherwise violated the rule of the law that day.”

According to the AP, the Department of Justice is considering putting Schaffer in the federal witness security program, as he may testify in related cases.

Authorities have charged 420 people in connection to the riots, which left five people—including a U.S. Capitol Police officer—dead.