Five people died in the violence, including a Capitol Police officer.
Supporters of US President Donald Trump clash with police officers in front of the Capitol Building in Washington DC on January 6.
"While the Department was prepared to neutralize and remove individuals or groups engaging in civil disobedience or violence among the demonstrators, it was quickly overwhelmed by the thousands of insurrectionists (many armed) who immediately and without provocation began attacking officers, bypassing physical barriers, and refusing to comply with lawful orders", she was quoted by Reuters as saying in her prepared remarks being delivered Thursday to the House Appropriations Committee.
The Capitol is the meeting place of the United States Congress and the seat of the legislative branch of the USA federal government.
"We know that members of militia groups that were present on January 6 have stated their desires that they want to blow up the Capitol and kill as many members as possible with a direct nexus to the State of the Union, which we know that date has not been identified, "Pittman said".
He also told them to protest peacefully but encouraged them to go to the Capitol and have their voices heard. 'This event was different because all judicial remedies for opposing election results had been exhausted and the only way for their candidate to win was for Congress to reject the Electoral College results'.
Officers were also warned, 'due to the tense political environment following the 2020 election, the threat of disruptive actions or violence can not be ruled out'.
Pittman's appointment put her among the few Black women police chiefs in the nation.
"Andrew Alan Hernandez, 44, was identified by a coworker who recognized him in a news photo of rioters who stormed the Capitol in an attempt to stop Congress from certifying Joe Biden's victory over incumbent Donald Trump in the November presidential election, according to an Federal Bureau of Investigation statement filed in U.S. District Court in Washington", reported Michael Finnegan.
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"So based on that information, we think that it's prudent that Capitol Police maintain its enhanced and robust security posture until we address those vulnerabilities going forward", she added.
Acting Capitol Police Chief Yogananda Pittman denies law enforcement failed to take warnings of violence prior to January 6 seriously because numerous people traveling to Washington before the Capitol insurrection were white.
Three days before the attack, the Capitol Police department's own security assessment warned that militia members, white supremacists, and other extremists were planning to come to Washington and target Congress in what they saw as a "last stand" to support Trump.
In recent weeks, a number of Capitol rioters have been turned in by acquaintances.
The acting head of the U.S. Capitol Police says about 800 pro-Trump rioters forced their way into the halls of Congress during the January 6 insurrection.
Officers had to evacuate House office buildings and also have businesses vacate premises and residents leave the area.
Officers were vastly outnumbered as thousands of rioters descended on the building, some of them wielding planks of wood, stun guns, bear spray and metal pipes as they broke through windows and doors and stormed through the Capitol. Many officers didn't know if they could use force and lacked guidance on how to stop the rioters, leaving some to improvise.
The department will also be looking at how less lethal munitions were deployed, as they were 'not as successful in dispersing insurrectionists in the attack, ' Pittman said.
'Additionally, the Department recognized that its training largely focuses on keeping unauthorized persons out of buildings on the Capitol Complex and not scenarios in which a building has been breached, ' she wrote. 'The Department will also be developing and pushing out additional training scenarios for our officers'. She said there may be legislation to address any inadequacies.
'It protected Congressional Leadership. 'At the end of a battle that lasted for hours, democracy prevailed'.