Officer Sicknick was responding to the riots on Wednesday, January 6, 2021, at the U.S. Capitol and was injured while physically engaging with protesters. He returned to his division office and collapsed.

https://www.npr.org/sections/congress-electoral-college-tally-live-updates/2021/01/07/954333542/police-confirm-death-of-officer-injured-during-attack-on-capitol

So total 5 deaths, the cop, 3 others who died of medical emergencies, e.g. heart attacks and Ashli Babbit who was murdered in cold blood inside the Capitol by someone under federal employment.

https://www.washingtonpost.com/local/dc-politics/capitol-riots-deaths/2021/01/07/19811264-5129-11eb-83e3-322644d82356_story.html