Four people are dead and 68 were arrested after President Donald Trump’s supporters charged into the US Capitol building on Wednesday ito disrupt certification of the 2020 election results.
The mob managed to only temporarily delay the certification count but inflicted considerable damage in the process.
Videos online show a woman trying to break through the panel of a door inside the Capitol building. Gunshots can be heard in the background.
Washington Metropolitan Police confirmed one woman, Ashli Babbitt, 35, was shot during confrontations between law enforcement and rioters inside the building.
Babbitt was a US Air Force veteran and a staunch Trump supporter.
“One plainclothes Capitol police officer discharged their service weapon, striking an adult female," acting police chief Robert Contee said.
"She was transferred to a local hospital where after all lifesaving efforts failed, she was pronounced deceased."
Three others died of unspecified medical emergencies.
They were: Benjamin Phillips, 50, from Ringtown, Pennsylvania; Kevin Greeson, 55, of Athens, Alabama; and Rosanne Boylen, 34, from Kennesaw, Georgia.
Fourteen Metropolitan Police officers were injured during the skirmishes.
As of Thursday morning, the police arrested 68 people for charges including unlawful entry and crossing a police line.
Four were charged for carrying pistols without licences. Carrying a gun openly in the district is prohibited.
Several others were arrested for curfew breaches after Washington Mayor Muriel Bowser imposed a curfew from 6pm local time.
The FBI asked for information to assist in identifying members of the mob who swarmed the Capitol.
Many across the country, including legislators, questioned why the mob was so easily able to gain entry.
Democrat congresswoman Ayanna Pressley called for a full investigation into the "terrorist acts and those individuals and agencies who enabled them".
Activists also criticised the police response to Wednesday’s events, saying it would have been much harder had it been a Black Lives Matter protest.
The police chief defended his department's response.
“We needed to make sure we had a safe situation," Mr Contee said.
"We had to contain the situation we were dealing with and the moment we were able to contain it, members were able to start effecting arrests.
"The initial arrest for curfew violations as well as for unlawful activity was at the Capitol.
"We started with arrests there and then we started moving methodically out from the US Capitol, making arrests."
As of Thursday, morning investigations were under way following the discovery of two pipe bombs near the Capitol.
One was found at the Republican National Committee, the other at the Democratic National Committee
Ms Bowser is expected to give further updates.