Updated

An alleged member of the Oath Keepers militia group who was "among the first five or six" rioters to enter the U.S. Capitol Building on Jan. 6 is the first person to agree to take a plea deal, Fox News has learned.

Jon Schaffer has also agreed to cooperate against others involved in the riot, officials said. 

Speaking in court Friday morning, a federal prosecutor told U.S. District Court Judge Amit Mehta that Schaffer was "among the first five or six" rioters to enter the Capitol during the Jan. 6 siege. Schaffer is also the frontman of the band Iced Earth.

This photo shows Jon Schaffer with other demonstrators who breached security and entered the Capitol as Congress debated the 2020 presidential election Electoral Vote Certification. (Photo by ROBERTO SCHMIDT / AFP) 

This photo shows Jon Schaffer with other demonstrators who breached security and entered the Capitol as Congress debated the 2020 presidential election Electoral Vote Certification. (Photo by ROBERTO SCHMIDT / AFP)  (Getty Images)

The central Indiana native who was photographed with the mob that stormed the U.S. Capitol is accused of spraying police officers with a pepper-based bear spray irritant, the FBI previously said.

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He was charged with several felony counts, including engaging in an act of physical violence and knowingly entering or remaining in any restricted building or grounds without lawful entry.

Schaffer, 53, pleaded guilty to obstruction of an official proceeding and entering and remaining in a restricted building or grounds with a deadly or dangerous weapon.

He faces up to 30 years in prison if convicted, but Mehta said Friday sentencing guidelines call for 41 to 51 months in prison.

Guitarist Jon Schaffer performs with the German-American power metal band Demons & Wizards during the Danish heavy metal festival Copenhell 2019 in Copenhagen. (PYMCA/Avalon/Gonzales Photo/Peter Troest/Universal Images Group via Getty Images)

Guitarist Jon Schaffer performs with the German-American power metal band Demons & Wizards during the Danish heavy metal festival Copenhell 2019 in Copenhagen. (PYMCA/Avalon/Gonzales Photo/Peter Troest/Universal Images Group via Getty Images) (Getty Images)

Schaffer is among more than 370 people facing federal charges in the deadly insurrection, which sent lawmakers into hiding and delayed the certification of Joe Biden's win in the presidential election. The Justice Department has indicated it is in separate plea negotiations with other defendants.

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"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. These actions are disgraceful and unacceptable" FBI Deputy Director Paul M. Abbate said in a press release announcement of the deal.

A sentencing hearing date has not yet been set. Schaffer was released and will be allowed some travel for work. He must stay out of Washington, D.C., other than for court-related matters and may not possess any firearms.

The Associated Press contributed to this report.