By 2:20 p.m., six minutes later, Mr. Khater has returned to the police line, where Officer Sicknick and his colleagues are standing behind a row of bike rack barricades. He stands just a few feet from Officer Sicknick, who can be seen wearing a blue Capitol Police jacket, bicycle helmet and black coronavirus face mask.

For about two minutes, Mr. Khater waits in the crowd, observing the police. Then, at 2:23 p.m., rioters try to pull the bike racks away from the officers. As a lieutenant in a white uniform fires a spray into the crowd, and a rioter charges in to attack a Metropolitan Police officer, Mr. Khater raises his arm over other rioters and sprays something toward Officer Sicknick.

A thin stream of liquid is visible shooting from a canister in Mr. Khater’s hand. It is unclear in the video what Mr. Khater is firing, and prosecutors have alleged that Mr. Tanios brought two smaller canisters of pepper spray to the Capitol in addition to two cans of Frontiersman bear spray.

Officer Sicknick reacts immediately to the spray, turning and raising his hand.