CNN  — 

Federal investigators are chasing thousands of leads in twin efforts to prosecute people involved in last week’s attack on the US Capitol and to try to prevent feared follow-up attacks in Washington and around the country.

But while the FBI has opened more than 160 case files in the six days since pro-Donald Trump rioters breached the US Capitol building, officials acknowledged Tuesday that the evidence gathered so far “is just the tip of the iceberg.”

“People are going to be shocked by some of the egregious contact that happened in the Capitol,” acting US Attorney Michael Sherwin said in reference to assaults on federal and DC police officers.

“So the picture is going to build. I think there’s a lot of misconceptions about what happened within the Capitol, and it’s going to come into laser focus I think over the next weeks and days,” he added.

At the same time, officials from the FBI and Department of Justice sought to reassure the American public Tuesday that they are up to the task on both fronts during a news conference that also laid bare the enormity of the challenge currently facing law enforcement agencies involved in both efforts.

“The FBI is quite familiar with large-scale, complex investigations … we are up to the challenge,” FBI Washington DC field office assistant director Steven D’Antuono said.

Sherwin echoed that point, telling reporters, “The scope and the scale of this investigation into these cases are really unprecedented not only in FBI history but probably DOJ history in which essentially the Capitol grounds outside and inside are essentially a crime scene.”

“It is not going to be solved in the coming months,” he added.

FBI director absent from briefing

FBI Director Christopher Wray did not attend the news conference, the first held by law enforcement officials since the attack took place nearly one week ago.

His absence has fueled questions about whether the Trump administration is treating the incident with the seriousness it requires, particularly after the President said earlier Tuesday that he believes he bears no responsibility for the attack carried out by his supporters.

Still, the officials who were present Tuesday vowed to leave no stone unturned as they treat the investigation of Capitol rioters similar to terrorism.

They also emphasized the fact that investigators have already charged 70 cases, and Sherwin said he believes that number will grow into the hundreds, and already arrested individuals may face more serious crimes.

“The numbers are going to geometrically increase,” Sherwin said.

Sherwin said he gave his prosecutors “marching orders” to pursue significant sedition and conspiracy cases as well related to the insurrection.

The FBI is also tracking money, travel records, movements of people and communications in addition to following tips from the public and footage and photos from the scene last Wednesday.

‘Grave concerns about ongoing and violent threats to our democracy’

After Tuesday’s presser, the Democratic chairs of five House oversight committee issued a joint statement to express their “grave concerns about ongoing and violent threats to our democracy.”

“It is clear that more must be done to preempt, penetrate, and prevent deadly and seditious assaults by domestic violent extremists in the days ahead.”

The House lawmakers did applaud FBI and DOJ officials for insisting they will prosecute every individual associated with the attack, but made clear that they viewed that promise as a good first step.

Sen. Rob Portman, an Ohio Republican, said “Trump bears some responsibility for what happened on January 6.”

“If our nation experiences additional violence and destruction at the hands of his supporters in Washington DC and state capitols around the country, and he does not directly and unambiguously speak out now when threats are known, he will bear responsibility,” Portman added.

‘The chatter is off the charts right now’

Portman’s comments reflect a growing concern among law enforcement officials in recent days that violent mobs’ success in breaching the Capitol has increased the potential for attacks because people may be emboldened to carry out violence.

“The chatter is off the charts right now,” one official said.

The sprawling probe spanning all 50 states in some ways is unprecedented, even in comparison to the investigations after the 9/11 attacks. That’s because federal investigators are grappling with a domestic radicalization problem, that presents complications due to First Amendment protections of political speech, different from radicalization tied to foreign terrorist groups.

Some of the intelligence the FBI, ATF and other agencies shared before last week’s attack has taken new importance, and has prompted federal investigators to conduct visits with people already on their radar and who have raised concerns about violence. Much of the online threats found in social media and other forums is thought to be aspirational, but the FBI and other agencies now are treating them more seriously, officials said.

Some of that occurred before the January 6 Trump rally, federal officials have said. The FBI worked with Washington’s Metropolitan Police to arrest a leader of the Proud Boys in the days before the Trump rally on a relatively minor charge, and then added charges when they found him carrying extended ammunition magazines that are illegal in the city. Prosecutors monitored hotels where some attendees were staying.

But there were efforts by some of the groups of concern to try to evade detection. On the day of the rally, members of the Proud Boys ditched their normal yellow and black attire and donned orange hats, and they were seen gathering near the Capitol grounds to coordinate their march to the building, according to a federal law enforcement official and video from the day.

D’Antuono also said agents are still investigating whether participants in the January 6 riot were looking to take members of Congress as hostages.

He noted the FBI is pursuing information about a person or people who helped to plant pipe bombs outside the Republican and Democratic headquarters last week.

He said the bombs were real and had timers. “We don’t know exactly why they didn’t go off,” he added.

Strike force for sedition charges

Meanwhile, Sherwin said national security and public corruption prosecutors on Monday organized into a “strike force” in the DC US Attorney’s Office to build sedition and conspiracy cases. Prosecutors had also spent all of Monday working with a federal grand jury to prepare indictments as well.

“Just yesterday our office organized a strike force of very senior national security prosecutors and public corruption prosecutors. Their only marching orders from me are to build seditious and conspiracy charges related to the most heinous acts that occurred in the Capitol, and these are significant charges that have felonies with a prison terms of up to 20 years,” Sherwin said.

He said the grand jury in Washington was “up and booked throughout the day” so prosecutors could present significant cases for indictment.

This story has been updated with additional developments.

CNN’s Katelyn Polantz contributed to this report.