Officer Brian D. Sicknick died at about 9:30 p.m. on Thursday, the Capitol Police said in a statement. He had been with the agency since 2008.

Mr. Sicknick was responding to the riots on Wednesday and “was injured while physically engaging with protesters,” the agency’s statement said, although officials didn’t immediately elaborate on the nature of his injuries or how he interacted with the crowd. After sustaining the injuries, Mr. Sicknick returned to his division office, collapsed, and was taken to the hospital.