The US Department of Justice will seek sedition and conspiracy charges after the siege at the US Capitol last week.
The department is treating its inquiry into the event as a "significant counter-terrorism or counter-intelligence investigation".
“We’re looking at significant felony cases tied to sedition and conspiracy,” the acting US attorney for the District of Columbia, Michael Sherwin, said on Tuesday.
Those felonies can carry prison sentences of up to 20 years.
"Regardless of if it was just a trespass at the Capitol or if someone planted a pipe bomb, you will be charged and you will be found," Mr Sherwin said.
"People will be shocked at the egregious acts committed.”
He said 170 cases had already been opened and more than 70 people charged.
Mr Sherwin expected this number to "grow into the hundreds" in coming weeks. But the investigation could take months.
Charges include simple trespassing and theft of mail and digital devices, to assault on officers and possibly murder.
The Justice Department is using “all tools” to find the perpetrators and is looking into "money, travel records, disposition, movement, communication records", Mr Sherwin said.
A special unit of prosecutors is giving priority to cases in which members of the media were assaulted.
"Some of those rioters specifically targeted members of the media and assaulted them,” Mr Sherwin said.
"Murder the media" was scratched into a door of the Capitol after the attack, The New York Times reported, and several journalists were assaulted, including an AP photographer who was shoved to the ground.
Five people died in the attacks, including a police officer. Washington is on alert in the days leading up to president-elect Joe Biden's inauguration next Wednesday.
The US Department of Defence has authorised up to 15,000 National Guard troops to be sent to the city by the Saturday before the event.