Former Capitol Police Chief Steven Sund sent an eight-page letter to House Speaker Nancy Pelosi and other Congressional leaders on Monday, providing a detailed account of the events leading up to the Jan. 6 riots as well as a detailed timeline of events as he saw them unfold on that day.
Pelosi immediately called for Sund to step down on Jan. 7. Later that day, Sund submitted a letter of resignation.
ABC News obtained a copy of the letter, which was first reported by The New York Times.
In the letter, Sund said he knew about the intelligence leading up to the violent event and explained why he relied on assessments, as well as his efforts to secure support before and during the incident, from the National Guard and other law enforcement partners.
"Perfect hindsight does not change the fact that nothing in our collective experience or our intelligence – including intelligence provided by FBI, Secret Service, Department of Homeland Security (DHS) and D.C. Metropolitan Police (MPD) – indicated that a well-coordinated, armed assault on the Capitol might occur on Jan. 6," Sund wrote.
Sund said that intelligence indicated that the Jan. 6 event would be similar to two previous post-election demonstrations from November and December, which he described as MAGA I and MAGA II. Though, he wrote, the assessment included language that "members of the Proud Boys, white supremacist groups, Antifa, and other extremist groups were expected to participate in the Jan. 6 event and that they may be inclined to become violent." He continues: "This was very similar to the intelligence assessment of the Dec. 12, 2020, MAGA II event." During both of those previous protests there was a "limited amount of violence and/or injuries to officers, and a limited number of arrests."
"Having previously handled two major post-election demonstrations successfully utilizing an action plan that was based on intelligence assessments that had proven to be credible, reliable, and accurate, we reasonably assumed the intelligence assessment for Jan. 6, 2021, was also correct."
On Jan. 4, the Capitol Police Intelligence and Inter-Agency Coordination Division "assessed "the level of probability of acts of civil disobedience/arrests occurring based on current intelligence information," as "Remote" to "Improbable" for all of the groups expected to demonstrate on Wednesday, Jan. 6, 2021," according to Sund.
Sund said he directed the department to be placed on "all hands on deck" status, which meant every sworn officer would be working. He also said he activated seven Civil Disturbance Unit platoons, approximately 250 officers, with four of those platoons equipped in helmets, protective clothing and shields.
"During the meeting, no entity, including the FBI, provided any intelligence indicating that there would be a coordinated violent attack on the United States Capitol by thousands of well-equipped armed insurrectionists," Sund wrote.
Sund said the Department of Homeland Security never issued a threat advisory about "violent extremists planning a coordinated attack on the U.S. Capitol" and noted that the "U.S. Secret Service planned to and did escort the Vice President of the United States to the Capitol on Jan. 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."
On the eve of the attempted insurrection, Sund said he sent an email to his leadership team to ensure that all officers were fully briefed to expect a "long day, large groups, and clashes that could possibly include violence."
As the crowd was attempting to breach the building, Sund wrote, the Capitol Police Dignitary Protection Division prepared to evacuate congressional leadership. Capitol Police "attempted to secure hallways to prevent the mob from advancing further into the building" and "initiated evacuations" of members of Congress to safe locations.
Sund maintained that the U.S. Capitol Police "did not fail" and that the department "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." He credited the bravery and heroism of Capitol Police officers who "outnumbered and against tremendous odds" managed to keep members of Congress safe.
"The entire intelligence community seems to have missed this," Sund wrote.
Pelosi announced on Jan. 15 she was appointing retired Lt. Gen. Russel Honoré, the same man who led the government response to Hurricane Katrina, to issue a report on Capitol security in relation to the riot.
"I have asked retired Lt. Gen. Russel Honoré to lead an immediate review of security infrastructure, inter-agency processes and command and control," Pelosi said at the time. "The general is a respected leader with experience dealing with crisis."
Sund did acknowledge that a "number of systems broke down" and that "officials or officers who violated policies or directives, or even their oath, need to be held accountable."
In closing, Sund pledged in the letter he "will do anything I can, and everything that is requested of me, to help ensure that an attack like Jan. 6, 2021, never happens again" and that he stands "ready, willing and able to assist in any effort."