The mass attack on the U.S. Capitol on Jan. 6 “was pre-planned, and involved participants … who came well equipped, coordinated, and prepared to carry out a violent insurrection,” former Capitol Police chief Steven Sund told senators at a hearing on Tuesday.

These criminals came prepared for war,” he added. “They came with their own radio system to coordinate the attack, as well as climbing gear and other equipment to defeat the Capitol’s security features.”

Sund said that he witnessed the rioters beating officers with “fists, pipes, sticks, bats, metal barricades, and flag poles.”

I’m sickened by what I witnessed that day,” Sund declared.

His description of the riot came as members of two Senate committees sought answers to key questions about the unprecedented events of that day.

Everyone knows — or believes they know — what happened: hundreds of supporters of then-president Donald Trump, including militant groups like the Proud Boys and the Oath Keepers, stormed the Capitol, trashing the building and threatening the lives of lawmakers, as well as the vice president.

At least five people did die, including a Capitol Police officer.

But why did it happen? How could it happen? Could it have been stopped before things turned so violent? And was it really all planned in advance and coordinated by groups leading the mob?

On Tuesday, in the first of what could become a months-long series of joint hearings on the roots of the riot, senators in the Homeland Security and the Rules committees put those questions and others to four law enforcement officials, three of whom resigned following that day’s events, reported the Washington Post.

Tuesday’s main witnesses included former House sergeant-at-arms Paul Irving and former Senate sergeant-at-arms Michael Stenger — neither of whom had spoken publicly about their decision-making before and during the riot — along with acting D.C. police chief Robert Contee and Sund, the ex-Capitol Police chief.

Contee said that more than an hour after D.C. police were summoned to the Capitol he was part of an emergency phone call that included leaders of the Capitol Police, the National Guard and the Department of the Army.

“I was surprised at the reluctance to immediately send the National Guard to the Capitol grounds,” Contee said, adding that he was “stunned” by the lack of urgency, The Hill reported.

More than 1,100 District police officers would ultimately respond to the attack, Contee said, and 65 of them were injured. A 66th would take his own life a few days later,” The Hill said.

But on the day of the riot, it seems the Pentagon dragged its collective feet on bringing in the Guard: no troops arrived arrived at the Capitol until 5:40 p.m., four hours after Sund had requested them.

Much of the testimony focused on perceived shortcomings of intelligence gathering before the pro-Trump mob began its attack.

“A clear lack of accurate and complete intelligence across several federal agencies contributed to this event, and not poor planning by the United States Capitol Police,” Sund said. “We rely on accurate information from our federal partners to help us develop effective security plans.”

Irving added: “Based on the intelligence, we all believed that the plan met the threat and that we were prepared. We now know that we had the wrong plan.” 

Sund’s testimony contradicted Irving’s on a key point: exactly when the call went out for the Guard to reinforce police trying to defend the Capitol.

“According to Sund, he called Irving at 1:09 pm on January 6 to tell him that National Guard troops were urgently needed at the Capitol,” reported The Guardian.

“But Irving claimed that Sund’s request did not come until after 2 p.m. The exact timing is crucial, given that Vice-President Mike Pence was escorted out of the Senate chamber at approximately 2:14 p.m., just minutes before the rioters reached the room.”

The hearing came almost seven weeks after the attack and more than a week after the Senate voted to acquit former President Donald Trump of inciting the insurrection by telling his supporters to “fight like hell” to overturn his election defeat, reported the Associated Press.

“Thousands of National Guard troops still surround the Capitol in a wide perimeter, cutting off streets and sidewalks that are normally full of cars, pedestrians and tourists,” the AP said.

Earlier in the session, the senators heard from Capitol Police Capt. Carnesysha Mendoza, who suffered chemical burns on her face and nearly had her arm broken while struggling to control the rioters.

Of the multitude of events I’ve worked in my nearly 19-year career in the department, this was by far the worst of the worst,” Mendoza said. “We could have had 10 times the amount of people working with us, and I still believe the battle would have been just as devastating.”