The FBI and the Department of Homeland Security downplayed or ignored “a massive amount of intelligence information” ahead of the January 6 2021, attack on the US Capitol, according to the chairman of a Senate panel that on Tuesday is releasing a new report on the intelligence failures ahead of the insurrection.

The report details how the agencies failed to recognize and warn of the potential for violence as some of then-President Donald Trump’s supporters openly planned the siege in messages and forums online.

Among the multitude of intelligence that was overlooked was a December 2020 tip to the FBI that members of the far-right extremist group Proud Boys planned to be in Washington, DC, for the certification of Joe Biden’s victory and their “plan is to literally kill people”, the report said.

The Senate Homeland Security and Governmental Affairs Committee said the agencies were also aware of many social media posts that foreshadowed violence, some calling on Mr Trump’s supporters to “come armed” and storm the Capitol, kill politicians or “burn the place to the ground.”

Michigan Senator Gary Peters, the Democratic chairman of the Homeland panel, said the breakdown was “largely a failure of imagination to see threats that the Capitol could be breached as credible”, echoing the findings of the September 11 commission about intelligence failures ahead of the 2001 terrorist attacks.

The report by the panel’s majority staff says the intelligence community has not entirely recalibrated to focus on the threats of domestic, rather than international, terrorism.

And government intelligence leaders failed to sound the alarm “in part because they could not conceive that the US Capitol Building would be overrun by rioters”.

Still, Mr Peters said, the reasons for dismissing what he called a “massive” amount of intelligence “defies an easy explanation”.

While several other reports have examined the intelligence failures around January 6, including a bipartisan 2021 Senate report, the House January 6 committee last year and several separate internal assessments by the Capitol Police and other government agencies, the latest investigation is the first congressional report to focus solely on the actions of the FBI and the Department of Homeland Security’s Office of Intelligence and Analysis.

In the wake of the attack, Mr Peters said the committee interviewed officials at both agencies and found what was “pretty constant finger pointing” at each other.

“Everybody should be accountable because everybody failed,” Mr Peters said.

Using emails and interviews collected by the Senate committee and others, including from the House January 6 panel, the report lays out in detail the intelligence the agencies received in the weeks ahead of the attack.

There was not a failure to obtain evidence, the report says, but the agencies “failed to fully and accurately assess the severity of the threat identified by that intelligence, and formally disseminate guidance to their law enforcement partners”.

As Mr Trump, a Republican, falsely claimed he had won the 2020 election and tried to overturn his election defeat, telling his supporters to “fight like hell ” in a speech in front of the White House that day, thousands of them marched to the Capitol.

More than 2,000 rioters overran law enforcement, assaulted police officers, and caused more than 2.7 billion US dollars in damage to the Capitol, according to a US Government Accountability Office report earlier this year.

Breaking through windows and doors, the rioters sent politicians running for their lives and temporarily interrupted the certification of the election victory by Biden, a Democrat.

Even as the attack was happening, the new report found, the FBI and Homeland Security downplayed the threat.

As the Capitol Police struggled to clear the building, Homeland Security “was still struggling to assess the credibility of threats against the Capitol and to report out its intelligence”.

And at a 10am briefing as protesters gathered at Mr Trump’s speech and near the Capitol were “wearing ballistic helmets, body armour, carrying radio equipment and military grade backpacks”, the FBI briefed that there were “no credible threats at this time”.

The lack of sufficient warnings meant that law enforcement were not adequately prepared and there was not a hardened perimeter established around the Capitol, as there is during events like the annual State of the Union address.