A former Argonne National Laboratory employee has admitted to assaulting law enforcement officers during the Jan. 6, 2021, riot.Robin Lee Reierson, 69, of Schiller Park, pleaded guilty Monday to a felony charge of assaulting, resisting or impeding certain officers.Reierson was among a group of rioters gathered in the West Plaza of the U.S. Capitol building, according to court documents. He used his body to push against a barrier and into a line of police officers, the documents said.He eventually left the West Plaza, but told other rioters “Don’t stop, keep going,” according to a statement from the U.S. Attorney's Office for the District of Columbia. Related Manteno man gets 2 years in prison for shoving officer, tossing mug at police during Capitol riot Related Southwest suburban residents plead guilty in Jan. 6 case About a week after the attack on the Capitol, someone sent a tip to the FBI that an employee of Argonne National Laboratory was possibly involved in the riot. Reierson was employed as a lead welder at Argonne for more than 40 years, but he no longer works there.The FBI matched images from videos to Reierson’s Illinois driver’s license and began surveillance of his home. Agents observed him leaving in a cargo van with the same Illinois license plates that tollway records indicate was driven to Washington on Jan. 5, 2021, and back to Illinois on Jan. 7, 2021. Related A list of every known Illinois resident charged in the U.S. Capitol breach The FBI arrested Reierson on Aug. 23, 2023. He was initially charged with assaulting an officer, obstruction of law enforcement, entering a restricted building and engaging in disorderly conduct with the intent of impeding Congress.Reierson is one of nearly 50 known Illinois residents to face federal criminal charges connected to the Jan. 6 attack.He will be sentenced by U.S. District Judge Reggie B. Walton on Oct. 16.