US Capitol police officer Brian Sicknick has died from injuries sustained during the storming of the building led by supporters of President Donald Trump, the force says.
Wednesday's dramatic breach of the Capitol was a stunning assault on American democracy at a time when Congress was certifying the victory of President-elect Joe Biden.
"Officer Sicknick was responding to the riots ... and was injured while physically engaging with protesters," US Capitol Police (USCP) said in a statement.
He died on Thursday after being taken to hospital following his collapse upon returning to his divisional office, they said.
Metropolitan homicide officials will investigate the death of officer Sicknick, who joined the unit in 2008, along with the USCP and its federal partners, police said.
Trump condemned the violence, saying rioters had defiled the seat of American democracy and must be held accountable.
Among four others who died on Wednesday were demonstrator Ashli Babbitt, an air force veteran who embraced right-wing conspiracy theories, who was shot by authorities.
Three other people - two men and a woman - who were on the Capitol grounds died as a result of unspecified "medical emergencies," Washington's Metropolitan Police Department said.