Sund also wrote it was clear to him that within minutes of the mob arriving at the west front of the Capitol, the “situation was deteriorating rapidly” and that the agency didn’t have the resources it needed to keep the Capitol secure without help from outside agencies.

An officer died during the fight for the Capitol, one later died by suicide and more than 140 others were injured. At least three other people died, including a woman shot by a Capitol Police officer as she climbed through a window into the Speaker’s Lobby. The assault on the capitol delayed the certification of election results and was the first time the building had been overrun since 1814.

Sund also provided a timeline for the aid he sought from local law enforcement agencies and National Guard units, and an accounting of the meetings he had after the perimeter had been breached while he sought assistance.

It took more than four hours for requested Guard troops to get sworn in at the Capitol, and more than 1,700 police officers from 18 nearby jurisdictions convened at the Capitol in the interim to clear the building of people and potentially hazardous materials. At least two officials, Army Lt. General Walter Piatt and House Sergeant at Arms Paul Irving, cited the “optics” or “visuals” of deploying the National Guard in their hesitance to deploy them, according to Sund’s accounting.

The tone of the letter at-times appeared defensive and Sund took issue with the use of the term “fail” to describe the US Capitol Police’s conduct that day.

“I do not believe that the US Capitol Police failed,” Sund wrote. “Greatly outnumbered and against tremendous odds, they kept the Members safe.”

The US Capitol Police force is part of Congress and has the sole responsibility for the building’s security. The agencies cited in Sund’s letter are part of the executive branch of government and don’t have authority to force USCP to take any action.

And if the US Capitol Police knew an armed insurrection was coming, it’s not clear that the best option would have been to staff up and prepare for battle, so the lack of intelligence is noteworthy but the responsibility to keep the building remained with US Capitol Police.

Sund said he did ask two of his supervisors, appointed by Congress, for more help before the day’s rally. They said no.

“I must add that I wish that before placing the blame on the USCP and on me as the Chief for the breach of the Capitol by an insurrectionist mob, more consideration would have been given to the impact of incomplete information provided by intelligence assessments, the denied National Guard request, and the subsequent delayed approval for National Guard assistance,” Sund wrote.

In the month since the insurrection, US Capitol Police have not held a single news conference. The department’s acting chief, Yoganada Pittman, testified to Congress in a closed-door session that was not not open to the public. Pittman was elevated to chief after Sund’s resignation and was a top deputy on the day of the insurrection. She also released a video statement on Friday afternoon, promising “significant changes to our operations, policies and procedures.”

None of the five members of Congress who received Sund’s February 1 letter have mentioned it or the information within it in publicly in the four days since it was sent.

What new details that have emerged have been through leaks from Congress, law enforcement agencies and the willingness of US Capitol Police officers to break department policy to speak with reporters.

A spokesperson for the FBI, the US Secret Service, and former Sergeant at Arms Paul Irving declined to comment. The chairman of the union representing US Capitol Police officers declined to comment.

Representatives for the Department of Homeland Security, DC Metropolitan Police and US Capitol Police did not respond to requests for comment. The former Senate Sergeant at Arms Michael Stenger could not be reached for comment.

Police expected ‘likelihood of violence’

As the police force prepared for the rally on January 6, two other recent pro-Trump rallies loomed in the minds of those responsible for securing the Capitol.

Both were located at the US Supreme Court building, next to the Capitol. Police referred to these as “MAGA I” and “MAGA II” and Sund wrote had police handled “both of those events successfully, utilizing an action plan that was based on intelligence assessments developed by us and our partner agencies.”

The inter-agency process used by Capitol Police to plan for these events resulted in an intelligence assessment and an action plan for both. Each event resulted in dozens of arrests. Four officers were injured in the first event and eight in the second.

Police expected “various extremist groups” at both events and a “likelihood of violence.” The action plan included use of the Capitol Police’s “civil disturbance” unit, the use of steel barriers for crowd control, extra security for Congress and coordination with other police agencies.

But the focus of the protests on the January 6 would be the Capitol building itself and Sund wrote that he expected the crowd to be different “in size and risk.”

The inter-agency process published an intelligence assessment of the event three days before the event, which included input from US Capitol Police intelligence officials as well as the FBI, US Secret Service, Department of Homeland Security and the DC Metropolitan Police Department.

On January 3, an assessment of the expected protests indicated the coming protest was “expected to be similar to the previous Million MAGA March rallies in November and December 2020, which drew tens of thousands of participants,” Sund wrote in his letter to Pelosi. The assessment indicated that the far-right Proud Boys and far-left Antifa groups were expected at the Capitol on the January 6 and “may be inclined to become violent.”

The assessment, reviewed by CNN, noted earlier arrests at the November and December rallies and the violence between pro-Trump and opposition groups. It noted an estimated increase in hotel bookings, up to double, compared to the December rally. It noted advice given to protesters to travel carry weapons and travel in large groups to discourage police from taking enforcement action.

The assessment noted the last-stand feelings surrounding the event, a concern over calls for protesters to show up armed, and that then-President Donald Trump had promoted two rallies where members of Congress were expected to speak and which were expected to draw the largest crowds.

It also noted a shift in who the protesters would target. In the previous two protests, Trump supporters clashed with counter protesters. But on January 6, Congress would be the target.

A day later, the US Capitol Police’s daily intelligence report assessed the risk of violence at these events as either “remote” or “improbable,” according to Sund’s letter. That day’s report noted “the Secretary of Homeland Security has not issued an elevated or imminent alert at this time.”

A copy of that daily intelligence briefing, reviewed by CNN, shows a scale of risk and each known event being assessed based on that scale. It’s not clear what, if anything, changed between the event assessment on January 3 and the daily intelligence report on January 4. No comparable risk-assessment scale was included in the event assessment on January 3.

“At no time during the previous MAGA I or MAGA II events did the crowd attempt to storm or attack the Supreme Court building, or the adjacent Capitol building, and based upon all available intelligence, nothing of that sort was expected to happen on January 6,” Sund wrote in his letter to Congress.

Sund said he ordered the department into an “all hands on deck” posture ahead of the event and expedited the shipment of riot helmets, meant to be available for the inauguration two weeks later. He also asked the Sergeant at Arms for both the House and Senate, who together with the Capitol Architect form the board that oversees the police department, to request the National Guard.

The sergeant for the House, Irving, said he “was concerned about the ‘optics’ and didn’t feel the intelligence supported it,” Sund wrote. The sergeant for the Senate, Stenger, suggested asking the Guard to be ready in case Sund needed them.

Irving and Stenger have since resigned. Sund also disclosed that members of Congress had been briefed on Capitol security before the event.

The day before the rally, Sund met with his oversight board and a dozen top police and military officials from across DC, to discuss both the January 6 rally and inauguration planning. No one present offered any new intelligence, Sund wrote.

“It should also be noted that the U.S. Secret Service planned to and did escort the Vice President of the United States to the Capitol on January 6, which it obviously would not have done if it believed there to be a threat of a violent insurrection at the Capitol building and on its grounds,” Sund wrote.

Mob like ‘nothing I have ever seen’ in career

At 7:15 a.m. ET on January 6, lines had already formed to attend the then-President’s rally at the Ellipse south of the White House, but an on-scene supervisor told Sund the group was compliant and that he didn’t observe any “concerning issues.” Sund went to his agency’s command center, he wrote.

Just before 1 p.m., someone found a pipe bomb near the Republican National Committee headquarters, and US Capitol Police responded to that. At the same time, a group approached the west front of the Capitol and started attacking police “immediately.”

“Their primary goal was to defeat our perimeter as quickly as possible and to get past the police line. This mob was like nothing I have seen in my law enforcement career. The group consisted of thousands of well-coordinated, well-equipped violent criminals. They had weapons, chemical munitions, protective equipment, explosives, and climbing gear. A number of them were wearing radio earpieces indicating a high level of coordination,” Sund wrote.

Officers who worked that day and who spoke to CNN criticized the use of those barriers, noting that they’re meant for compliant crowds and could be easily used as weapons by those intent on violence. It’s not clear why those were the preferred method of crowd control when it was clear, by Sund’s actions, that there was at least some expectation of violence.

Sund wrote that he asked Irving and Stenger, the sergeants at arms, for the National Guard at 1:09 p.m. Irving said he “needed to run it up the chain of command,” Sund wrote. At 1:50 p.m., and without an answer from Irving and Stenger, he contacted Gen. William Walker, of the DC National Guard, and said he was expecting approval for his request. At 2:10 p.m., Irving authorized the formal request.

An hour into the fight, about 1:50 p.m., a second bomb was found, as well as a vehicle with Molotov cocktails and a gun, all near the Capitol grounds. This caused police to divert “extensive USCP resources” and the evacuation of two congressional buildings.

“I believe all of this was part of a coordinated plan related to the attack on the Capitol,” Sund wrote. It was at this time he asked for mutual aid from other police agencies, which resulted in 1,700 officers from 18 agencies converging on the Capitol.

While police were fighting to keep protesters out, other officers began to evacuate congressional leadership and directed officers to secure the House and Senate.

Twenty minutes after Sund’s supervisors approved the request for the Guard, Sund learned he needed Pentagon approval to deploy the Guard. It’s not clear why it wasn’t known prior to January 6 that this would be required in the event US Capitol Police would need the help.

At 2:22 p.m., according to a timeline released by the Department of Defense, the secretary of the Army, DC’s mayor and other police officials had a phone call to discuss additional guard support for US Capitol Police. Sund’s letter notes a phone call with officials about the same time.

At 2:30 p.m., Pentagon officials met separately to discuss the request. According to the Department of Defense timeline, the Pentagon approved deploying roughly 1,100 guard members to the Capitol about 3:04 p.m. At this point, US Capitol Police and DC Metropolitan Police had been fighting insurgents at the Capitol for two hours.

It appears the Guard wasn’t approved until Stenger, the Senate Sergeant at Arms, got then-Majority Leader Mitch McConnell to call the secretary of the Army, according to Sund’s letter.

The first guardsmen weren’t sworn in at the Capitol for more than four hours after the initial request Sund made to his supervisors, and more than three hours after Stenger and Irving approved the request, around 5:40 p.m.  The Department of Defense timeline also notes the arrival of more than 150 guard members at the Capitol at 5:40 p.m.

“I still cannot fathom why in the midst of an armed insurrection, which was broadcast worldwide on television, it took the Department of Defense over three hours to approve an urgent request for National Guard support,” Sund wrote.

Incoming officers were given two assignments: secure the perimeter and foundation of the Capitol and clear the Capitol and conduct a “top to bottom sweep” of the building. The goal, Sund wrote, was to “facilitate the safe and expeditious return of the Members of Congress to complete their certification of the electoral votes.”

‘The entire intelligence community seems to have missed this’

Almost five hours after the fight began, Sund briefed Pence on the security situation. Pence called Pelosi, and Sund advised that both chambers could reopen by 7:30 p.m., he wrote. Sund also briefed other members of congressional leadership around 6:30 p.m.

The Senate reconvened at 8 p.m. and the House at 9 p.m. Scores of people have been arrested and are facing federal charges in connection with the attack on the Capitol that day.

Toward the end of the letter, Sund acknowledged a breakdown in some systems, “all of which can be rectified with more resources, better training, updated policies, and accountability.” He did not specify which systems failed. But he again pointed to the lack of intelligence, noting officials didn’t predict an “armed assault” on the Capitol.

“What occurred on January 6th cannot be considered under any circumstances a protest, a rally, or civil disobedience,” Sund wrote. “This was a well-planned, coordinated, armed insurrection at the United States Capitol. The USCP does not have the manpower, the training, or the capabilities to handle an armed insurrection involving thousands of individuals bent on violence and destruction at all costs.”

In a statement to CNN on Saturday night, an Army spokesperson said that the “preparation and posture of the D.C. National Guard was based on the single request for assistance the Pentagon received from the D.C. Mayor for limited support, primarily for street closures and crowd control involving 340 DCNG at various locations around the district to facilitate and protect peaceful demonstrations.”

The Department of Defense Inspector General is now reviewing the details of the preparation for and response to January 6 attack on the Capitol, the statement continued.

“We intend to allow that process to proceed independently by not commenting further,” the Army spokesperson said.

This story has been updated with a statement from the Army.