“I think the scope and scale of this investigation and these cases are really unprecedented, not only in FBI history but probably DOJ history,” Acting US Attorney Michael Sherwin said in a media briefing on Tuesday.

“The Capitol grounds outside and inside are… a crime scene.”

Sherwin said people are “going to be shocked by some of the egregious contact that happened in the Capitol”.

“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.”

Sherwin said 70 criminal cases have been filed to date.

While many of them involve people whose photos went viral on social media, such as one of a man pictured sitting at the desk of a staffer of House Speaker Nancy Pelosi, he said more serious charges are coming and a grand jury has been reviewing the cases.

“We’re looking at significant felony cases tied to sedition and conspiracy,” Sherwin said, noting his office has launched a strike force whose marching orders are to build criminal cases around such charges.

He said other strike forces have been formed to focus on assaults on law enforcement and members of the media.

“The range of criminal conduct is really … unmatched in any type of scenario that we’ve seen,” Sherwin said, noting it runs the gamut from “simple trespass” and “theft of mail” to “felony murder and even civil rights excessive force”.

Investigators are combing social media images that showed hundreds of people swarming the building, attacking police, stealing computers and artifacts and smashing windows.

Steven D’Antuono, the assistant director in charge for the FBI’s Washington, DC office, said the bureau has been combing through more than 100,000 photos, video and other tips it has received since last week.

The FBI has been releasing photos of suspects and seeking help from the public. Recently, it released images of someone who is suspected of planting pipe bombs at the headquarters of the Democratic and Republican national committees.

In New York, Aaron Mostofsky, whom news outlets identified as the son of New York Supreme Court Judge Shlomo Mostofsky, was arrested after photos of him at the US Capitol dressed in a fur costume appeared in an article by the New York Post.

He was charged with theft of government property, unlawful entry, knowingly impeding government business and disorderly conduct. He was released on a $US100,000 ($A130,000 ) bail following a hearing in Brooklyn on Tuesday.

Louis Capriotti, 45, of Illinois, was also charged on Tuesday for leaving a threatening voice mail to a member of Congress in late December.

Several other suspects appeared in federal courts on Tuesday, including Lonnie Coffman, whom a judge ordered be detained after police discovered explosives and guns in his car, along with notes containing the name of a member of Congress.

Military leaders condemn Capitol assault

The US military’s Joint Chiefs of Staff, the uniformed leaders of the military branches, put out a rare message to service members saying Capitol riots were an assault on America’s constitutional process and against the law.

The joint message broke nearly a week of silence by the military leaders after the assault on the Capitol by supporters of President Donald Trump sent lawmakers into hiding and left five people dead.

While a number of Trump’s cabinet members including acting Defense Secretary Chris Miller condemned the storming, the top US general, Chairman of the Joint Chiefs of Staff General Mark Milley, was silent until now.

“The violent riot in Washington, DC on January 6, 2021 was a direct assault on the US Congress, the Capitol building, and our Constitutional process,” the seven generals and one admiral said in an internal memo to troops, adding the military remained committed to protecting and defending the Constitution.

“The rights of freedom of speech and assembly do not give anyone the right to resort to violence, sedition and insurrection,” the memo, seen by Reuters, said.

The military leaders said President-elect Joe Biden would be inaugurated on January 20 and become their commander in chief.

“Any act to disrupt the constitutional process is not only against our traditions, values, and oath; it is against the law.”

US officials said Milley had not commented on last week’s events because he wanted to stay out of politics.

The silence was in sharp contrast with June, when Milley made a controversial walk to a church with Trump after law enforcement officers backed by National Guard troops used tear-inducing chemicals and rubber bullets to clear the area of peaceful protesters

Some service members have privately expressed concern that senior leaders did not provide direction in the aftermath of the attack on American democracy on Wednesday.

There has also been a renewed focus on extremism within the US military after the Capitol storming, with a large proportion of service members being white and male.

The army told Reuters on Tuesday that it was working with the FBI to see if any attackers were current service members and with the Secret Service to see if any of the nearly 10,000 National Guard troops securing Biden’s inauguration would need additional screening.

-with AAP