Mr. Khater and Mr. Tanios were seen on video early in the afternoon standing five to eight feet away from police officers, including Officer Sicknick, the F.B.I. said.
In a video of the attack, Mr. Khater said, “Give me that,” and then reached into Mr. Tanios’s backpack, the F.B.I. said. Mr. Tanios protested that it was too early, apparently to attack the officers with the spray. Mr. Khater countered that he had just been sprayed and held up the can of chemical spray.
At 2:23 p.m., as other rioters began to pull away a barrier between them and the Capitol, Mr. Khater aimed his spray can toward officers, the F.B.I. said, citing video footage including a body camera worn by an officer from Washington’s Metropolitan Police Department. The officers reacted “one by one, to something striking them in the face,” the F.B.I. said. “The officers immediately retreat from the line, bring their hands to their faces and rush to find water to wash out their eyes.”
They were unable to defend the Capitol for at least 20 minutes while they recovered, video showed, according to the F.B.I. Two other officers who were assaulted “described the spray to their face as a substance as strong as, if not stronger than, any version of pepper spray they had been exposed to during their training as law enforcement officers,” the F.B.I. said, and one said she had scabs on her face for weeks.
Officer Sicknick was later rushed to a hospital, where he died. Investigators opened a homicide investigation immediately after the death of the officer, a 42-year-old Air National Guard veteran who served in Saudi Arabia and Kyrgyzstan.
Both officers and rioters deployed spray, mace and other irritants during the attack. Given that evidence, prosecutors brought assault charges rather than a murder charge, law enforcement officials said, speaking on the condition of anonymity to discuss a continuing investigation.
It remains unclear whether Officer Sicknick died because of his exposure to the spray. On Jan. 7, the day that he died, the Capitol Police said in a statement that he “was injured while physically engaging with protesters” at the riot and then “returned to his division office and collapsed.”