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.”
In the hours after Officer Sicknick was taken to the hospital, Capitol Police officials initially said that he had been struck with a fire extinguisher, but later said that his death was not caused by blunt force trauma. In the following days, investigators homed in on the potential role of an irritant as a primary factor in his death.
The arrests came weeks after investigators pinpointed one of the men in a video of the riot, in which he was seen attacking officers with an unidentified spray, according to two law enforcement officials.
After the F.B.I. posted fliers with photographs of Mr. Khater and Mr. Tanios seeking information about the Jan. 6 attack, a tipster told the F.B.I. that the two men had grown up together in New Jersey.