Sicknick was a member of the Capitol Police's First Responder Unit. During the attack on the U.S. Capitol on January 6, 2021, Sicknick was on duty outside at the Capitol's west side, specifically the lower west terrace, on the front line facing protesters. As tensions increased, both police and some of the rioters deployed chemical spray and other irritants. At about 2 p.m., Sicknick and perhaps two fellow officers were sprayed and became unable to perform their duties for about 20 minutes.