A handful of Republicans have already said they'll join the effort to impeach Trump, a number that could grow as the vote nears.
"The Capitol grounds outside and inside are... a crime scene," acting U.S. Attorney Michael Sherwin said.
Some of the more than 50 defendants in the federal district and superior courts have been charged with gun-related offences.
``We must take action,'' House Speaker Nancy Pelosi declared Friday on a private conference call with Democrats.
The statement was accompanied by an image of a masked suspect wearing gloves and a hooded sweatshirt, carrying an object.
The U.S. Capitol Police said Officer Brian D. Sicknick was injured "while physically engaging with protesters" during the Wednesday riot, later dying in hospital.
Education Secretary Betsy DeVos and Transportation Secretary Elaine Chao are among the growing list of officials who are abandoning Trump after his supporters stormed the Capitol.
A violent siege of the U.S. Capitol interrupted the proceedings and appeared to force some Republicans to back down from plans to object to multiple states' electors.