US prosecutors said there was “strong evidence” that the rioters who swarmed the Capitol last week intended to target government officials for capture and assassination.

The detail came in a court filing against one of the defendants arrested in the aftermath of the attack, Jacob Anthony Chansley, the so-called Qanon Shaman who was pictured wearing a furry horned hat and face paint during the assault.

“Strong evidence, including Chansley’s own words and actions at the Capitol, supports that the intent of the Capitol rioters was to capture and assassinate elected officials in the United States government,” prosecutors said in the filing in Arizona federal court.

“Chansley left a note on the Senate Chamber dais, where vice-president Mike Pence had been presiding over the session just minutes before, warning ‘it’s only a matter of time, justice is coming,’” the filing said.

Prosecutors said that while Mr Chansley said the note was not meant as a threat, “the government strongly disagrees”.

The filing underscores the serious nature of the allegations that prosecutors are pursuing in what they have described as an “unprecedented” investigation into the attack, which has already led to dozens of charges.

Michael Sherwin, the acting US attorney for Washington, said at a briefing on Friday that the justice department had “no evidence” at the moment of “kill-capture teams” targeting lawmakers, but that there were “breadcrumbs” of “co-ordinated activity” among different individuals inside the Capitol.

Mr Sherwin said it would take “weeks, if not months, to find out the actual motivations of some of those groups”.

As of Friday morning, the Department of Justice had opened 98 criminal cases involving the events of January 6, and was expected to open 300 investigations into subjects related to the violence by the end of the day.

Federal prosecutors had also seen “indications that law enforcement officers, both former and current, maybe who have been off-duty” had been “participating in this riot activity”, Mr Sherwin said. 

“This is an unprecedented incident,” said Steven D’Antuono, FBI assistant director. “If this was a football game we would be in the first quarter.”

Internal watchdogs overseeing several US government agencies have launched reviews into the events leading up to last week’s deadly assault on the Capitol, as security measures around Washington and other state capitals were tightened ahead of Joe Biden’s inauguration next week.

The inspectors-generals at the departments of justice, homeland security, defence and interior announced on Friday the co-ordinated probes into their respective agencies amid the fallout from the rampage, which resulted in five deaths.

The DoJ’s watchdog said it would examine intelligence sharing with the Capitol Police and other agencies, and whether procedural weaknesses had hampered its response. The Pentagon inspector-general would examine requests made for military support leading up to the riots and whether the department’s response was “lawful and supported by requirements according to regulations and acceptable guidance”. 

Washington has drastically tightened security around the US capital ahead of the January 20 inauguration, including suspending tours of the Washington Monument, closing the Capitol to the public on inauguration day and deploying thousands of armed members of the National Guard to the streets. 

Nancy Pelosi, the speaker of the US House of Representatives, said on Friday that she had asked Russel Honoré — a retired lieutenant general in the US army who worked with House leadership during the response to Hurricane Katrina — to conduct “an immediate review of the Capitol’s security infrastructure, inter-agency processes and procedures, and command and control”.

Christopher Wray, FBI director, has warned of the risk of “potential armed protests” surrounding the inauguration, saying government buildings and officials in Washington and in state capitals appear to be the targets for extremist groups.

Jake Sullivan, Mr Biden’s incoming national security adviser, met on Wednesday with top FBI and US Secret Service officials for a briefing on the known threats and to plan to protect the president-elect, according to a person briefed on the matter. The preparations include detailed plans for the transition of power should violence occur during Mr Biden’s oath-taking or inaugural address.

Law enforcement agencies have also come under close scrutiny over failures to guard the Capitol last week, including the Capitol police, whose inspector-general has suspended all other work to focus solely on conducting a sweeping review of the force, two people briefed on the investigation said on Thursday. Steven Sund, the force’s outgoing chief, submitted his resignation in the aftermath of the attack.