(CNN) The House Select Committee investigating the January 6 attack will hear testimony Tuesday from four police officers who were on the front lines that day as rioters supporting then-President Donald Trump violently stormed the US Capitol in an attempt to stop lawmakers from certifying President Joe Biden's electoral win.
The hearing will mark the first time the panel will have public testimony, and will kick-start its efforts to investigate the events on January 6.
The four officers testifying -- DC Metropolitan Police Officers Daniel Hodges and Michael Fanone, plus Capitol Police Officer Harry Dunn and Sgt. Aquilino Gonell -- have shared their stories publicly before, which include accounts of being beaten with a flagpole, being the target of racist slurs, being crushed in a door and being tased by the rioters.
During Tuesday's hearing the officers will again describe what they experienced on January 6, according to a source familiar with their plans, who told CNN that the testimony will be "quite vivid" at times.
The witnesses will also raise questions for the committee to consider, stemming from how officers are still grappling with the physical and psychological wounds they endured more than six months ago and the care that they are, or are not, receiving, the source added.
This is what we know about the four officers who are set to testify:
Of the hundreds of police officers who defended the Capitol on January 6, none has become more outspoken than Fanone. He has met with lawmakers, publicly supported the creation of a bipartisan commission and slammed Republicans who whitewashed the violence of that day.
CNN exclusively obtained Fanone's body-worn camera footage, which shows how he was pulled into the crowd, beaten with a flagpole and repeatedly tased with his own Taser. Rioters stole his badge and grabbed at his service gun. When rioters said they should "kill him with his own gun," Fanone pleaded with the mob and told them, "I have kids," according to the video.
Four people were charged in connection with the assault, including one man who is accused of using the Taser. Fanone lost consciousness, suffered a heart attack and was hospitalized after the clashes, according to court filings. These defendants have pleaded not guilty and are in jail while awaiting trial. Prosecutors have said they're preparing plea deals for some of them.
"I want people to understand the significance of January 6. I want people to understand that, you know, thousands of rioters came to the Capitol hell-bent on violence and destruction and murder," Fanone previously told CNN.
Dunn has repeatedly spoken out about how he and his fellow Black officers are still grappling with their harrowing experience on January 6, when they endured racist attacks from insurrectionists during an assault on the US Capitol.
"The Black officer struggle was different as in, like I said, we fought against not just people that were, that hated what we represented, but they hate our skin color also," Dunn told CNN's Don Lemon during a March interview. "That's just a fact, and they used those words to prove that. They showed that they hated us and they hated our skin color."
Flags, signs and symbols of racist, White supremacist and extremist groups were displayed along with Trump 2020 banners and American flags at the riot. Black officers played a key role in defending lawmakers during the attack.
Dunn is the only Black officer scheduled to appear before the committee on Tuesday.
Last week, Fox News host Tucker Carlson sought to undermine Dunn's credibility, claiming without evidence that he "is an angry, left-wing political activist."
"Dunn will pretend to speak for the country's law enforcement community, but it turns out Dunn has very little in common with your average cop," Carlson said on his show.
The comments prompted an immediate response from Dunn's lawyers.
"Tonight Fox News allowed its host Tucker Carlson, who has not served a day in uniform, whether military or law enforcement, to criticize the heroism and service of African-American US Capitol Police Officer Harry Dunn," attorneys David H. Laufman and Mark S. Zaid said in a statement following the segment.
"Our client has served 13 years in law enforcement and on January 6, 2021, fought against an insurrectionist violent crowd -- no doubt many of them Carlson's supporters -- to protect the lives of our elected officials, including Vice President Pence," they wrote.
Gonell was beaten with a flagpole while defending the Capitol on January 6. His hand was sliced open. And he was hit with so much chemical spray that the liquid soaked through to his skin.
During intense hand-to-hand combat with rioters on the west front of the Capitol, there were moments where Gonell thought he might die.
"They called us traitors. They beat us. They dragged us," Gonell told CNN last month in his first interview about the violence he had experienced and witnessed. "And I could hear them, 'We're going to shoot you. We're going to kill you. You're choosing your paycheck over the country. You're a disgrace. You're a traitor.' "
Gonell said the FBI has asked him to view video of the attack to help identify the rioters. It's still difficult for him to watch footage of the events, he said during the same interview, having to relive the battles he fought while he was under assault.
He still has a vivid memory of what he faced: of the pepper spray that forced him and other officers from the front line, of the American flag poles, rocks and even guardrails pried from the inaugural stage that were used to attack officers, and of the struggle to keep the flood of insurrectionists from forcing their way through the door he was guarding.
"I bled, I sweat and I fought to prevent those people coming in through that entrance," Gonell said during the interview. "We got pushed back all the way to the magnetometer by the second door. And just to regain that space took us about another hour. We literally were fighting inch by inch. And to move one step, that was a 10-minute, 15-minute ordeal."
Hodges' struggle with the pro-Trump rioters became one of the most well-known scenes from the insurrection. A few days after the attack, harrowing footage emerged showing him crushed in a doorway between a massive press of rioters and the police line, writhing and screaming in pain. The video shows one of the rioters grabbing at Hodges' helmet and trying to rip it off.
In recent weeks, the Justice Department released several new videos from this skirmish, which unfolded in a tunnel near the still-unfinished staging area for Biden's inauguration. The Justice Department made the clips public only after CNN and other outlets sued for access.
The footage was part of the criminal cases against several people accused of participating in the attack on police in the tunnel area. One man, Patrick McCaughey, was specifically charged with assaulting Hodges with a stolen police shield and grabbing his helmet. He pleaded not guilty.