The Federal Bureau of Investigation said it had found that Mr. Alstrup “was employed” by the State Department as a diplomatic security officer. As part of that work, an F.B.I. agent wrote, Mr. Alstrup was “familiar with providing security and protection for high-ranking government officials or sensitive locations, like embassies.”
The F.B.I. also found posts that Mr. Alstrup had made on social media placing him outside the Capitol building that day.
Mr. Alstrup’s supervisor identified him in photos taken inside the Capitol, where, according to the affidavit, Mr. Alstrup spent about 28 minutes, including in the Crypt at the center of the building, before leaving through the Senate Wing’s doors.
While inside, Mr. Alstrup stood before a broken window and took photos of other rioters as they entered and left the building, court documents said.
After he left the Capitol, body-camera footage from a Metropolitan Police Department officer picked up Mr. Alstrup as well, the affidavit said.