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The House select committee investigating the Jan. 6 attack on the Capitol is holding its first hearing Tuesday, kicking off what is likely to be a politically charged and contentious several months focusing on the violent day.

The Tuesday hearing focuses on "The Law Enforcement Experience on January 6th." The four witnesses at the hearing are Private First Class Harry Dunn and Sergeant Aquilino Gonell of the U.S. Capitol Police, and Officers Michael Fanone and Daniel Hodges of the Metropolitan Police Department. They provided detailed and emotional testimony about the attack on the Capitol. 

"To be honest, I did not recognize my fellow citizens who stormed the Capitol on Jan. 6 or the United States they claimed to represent," Gonell, an immigrant and Army veteran, said. "The rioters called me traitor, a disgrace, and shouted that I, I, an Army veteran and police officer, should be executed."

"I heard specific threats to the lives of Speaker Nancy Pelosi and also Vice President Mike Pence," Gonell added, saying that he officers "fought hand to hand, inch by inch, to prevent an invasion of the Capitol by a mob intent on subverting our democratic process."

Gonell said that the attackers were shouting, 'Trump sent us. Pick the right side."

Trump supporters try to break through a police barrier, Wednesday, Jan. 6, 2021, at the Capitol in Washington. As Congress prepared to affirm President Joe Biden's victory, thousands of people gathered to show their support for former President Donald Trump and his false claims of election fraud. (AP Photo/John Minchillo)

Shortly after the hearing began, Chairman Bennie Thompson, D-Miss., – who emphasized that at least one rioter said he was at the Capitol to "overthrow the government" and that others chanted "hang Mike Pence" – played video of the violence that played out in the building. 

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The graphic video showed rioters pushing through police barricades; saying "f--- you police;" played panicked police radio tape; included graphic body cam footage; and showed violent crowds overwhelming officers as they pushed toward the inside of the Capitol. 

Also in the video were the gallows set up outside the Capitol and rioters saying they were "coming for" House Speaker Nancy Pelosi, D-Calif., and former Vice President Mike Pence, who they called a "traitor." The video closed with one person saying, "we need 30,000 guns up here," and another person saying, "next trip." 

"He will be back, he warns us. It's just chilling," Thompson said. "We need to understand how and why the big lie festered… And we need to figure out how to fix the damage." 

Rep. Liz Cheney, R-Wyo., who is a vocal critic of Trump, followed Thompson with comments lamenting that a bill for a special commission modeled on the 9/11 Commission failed in the Senate. But, she said, the committee must investigate the events of Jan. 6 anyway. 

"We must know what happened here at the Capitol," she said. "We must also know what happened every minute of that day in the White House. Every phone call. Every conversation. Every meeting leading up to during and after the attack."

In this Wednesday, Jan. 6, 2021 file photo, supporters of former President Donald Trump scale the west wall of the U.S. Capitol in Washington. (AP Photo/Jose Luis Magana, File)

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Cheney added: "We must issue and enforce subpoenas promptly. We must get to the objective truth. We must overcome the many efforts we are already seeing to cover up and obscure the facts."

Other officers detailed the physical violence and verbal abuse from the pro-Trump mob. 

"I was electrocuted again and again and again with a taser. I am sure I was screaming but I don't think I could even hear my own voice," Fanone said. He also said "the fighting in the West Terrace Tunnel was nothing short of brutal." 

"The mob of terrorists were coordinating their efforts… shouting ‘heave, ho,’ as they synchronized pushing their weight forward crushing me further against the metal doorframe," MPD Officer Daniel Hodges said. "A man in front of me grabbed my baton… he bashed me in the head and face with it, rupturing my lip and adding additional injury to my skull." 

Fanone said to Rep. Zoe Loftren, D-Calif., that rioters "tortured" him until he shouted that he had kids, at which point some rioters "intervened on my behalf." He later fell unconsious from the beating. 

Following that comment from Fanone, Rep. Adam Kinzinger, R-Ill., was choked up. 

"I never expected today to be quite as emotional for me as it has been," he said. "I think it's important to tell you right now, though, you guys may like individually feel a little broken. You guys all talk about the effects you have to deal with… but you guys won. You guys held." 

One woman in a pink MAGA shirt yelled, 'you hear that guys? This n------ voted for Joe Biden.' Then the crowd, perhaps around 20 people, joined in streaming, 'boo, f------ n-----

— Private First Class Harry Dunn, U.S. Capitol Police

"I'm a law enforcement officer and I do my best to keep politics out of my job. But in this circumstance, I responded, well I voted for Joe Biden. Does my vote not count? Am I nobody? That prompted a torrent of racial epithets," Dunn said. "One woman in a pink MAGA shirt yelled, 'you hear that guys? This n------ voted for Joe Biden.' Then the crowd, perhaps around 20 people, joined in streaming, 'boo, f------ n-----."

"I feel like I went to hell and back to protect them and the people in this room. But too many people are telling me now that hell doesn't exist... The indifference shown to my colleagues is disgraceful," Fanone added. "Nothing, truly nothing, has prepared me to address those elected members of our government who continue to deny the events of that day and in doing so betray their oath of office."

Thompson leads six other Democrats and two Republicans – Cheney, and Kinzingerl. The pair are the only Republicans on the committee after Pelosi refused to seat Reps. Jim Jordan, R-Oho, and Jim Banks, R-Ind., because they are too closely aligned with former President Donald Trump. 

 The indifference shown to my colleagues is disgraceful… Nothing, truly nothing, has prepared me to address those elected members of our government who continue to deny the events of that day and in doing so betray their oath of office.

— Officer Michael Fanone, Metropolitan Police Department

"Unfortunately, Speaker Pelosi will only pick people onto the committee that will ask the questions she wants asked," McCarthy said at a Tuesday press conference. "That becomes a failed committee and a failed report – a sham that no one can believe."

Republicans plan to hold their own investigation into Jan. 6.

But Kinzinger and Cheney – as well as Pelosi, who appointed them – insist that the committee will remain nonpolitical in its mission.

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"This moment requires a serious, clear-eyed, non-partisan approach. We are duty-bound to conduct a full investigation on the worst attack on the Capitol since 1814 and to make sure it can never happen again," Kinzinger said in a statement after being appointed to the committee. 

In this Jan. 6, 2021, file photo, smoke fills the walkway outside the Senate Chamber as supporters of former President Donald Trump are confronted by U.S. Capitol Police officers inside the Capitol in Washington. Far-right social media users for weeks openly hinted in widely shared posts that chaos would erupt at the U.S. Capitol while Congress convened to certify the election results. Republicans allege that Speaker Nancy Pelosi, D-Calif., should have seen those signs and fortified the Capitol. (AP Photo/Manuel Balce Ceneta, File)

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The committee investigation will likely last into 2022, a midterm election year. This makes it a probably target for former President Donald Trump as he continues to become more active on the campaign trail for Republican candidates. The former president assailed the committee in a Monday statement.

"Will Nancy investigate herself and those on Capitol Hill who didn’t want additional protection, including more police and National Guard, therefore being unprepared despite the large crowd of people that everyone knew was coming?" Trump said. Other Republicans like McCarthy often make this same point. 

The Tuesday hearing is the first for the select committee but it is not nearly the first time Congress has looked into the Jan. 6 attack. There have been more than a dozen hearings on the attack since the winter, not including the 25 hours the Senate spent on the matter during Trump's impeachment trial.  

Fox News' Jason Donner and Chad Pergram contributed to this report.