Demonstrators gathered outside the U.S. Capitol on Thursday ahead of the House select committee's first prime-time hearing of its Jan. 6 investigation.

Participants held signs reading, "Not above the law."

The panel is looking to explain what it calls a "coordinated, multi-step effort" by Trump and his supporters to overturn his 2020 election loss.

From legal action to name-calling, Trump continues to try to discredit the House select committee as the panel prepares to go public with its findings in prime time.

"January 6th was not simply a protest, it represented the greatest movement in the history of our Country to Make America Great Again," Trump said in a string of posts hours ahead of the hearing on Truth Social, the social media platform his team launched after Twitter permanently suspended him in the wake of the Capitol siege "due to the risk of further incitement of violence."

Click here for more on how Trump has deployed an arsenal of rhetoric to recast what happened and undermine the investigation.

Three rioters convicted on federal charges for participating in the Capitol attack appeared in court just hours ahead of the prime-time event and asked for mercy before federal judges deciding their punishments.

"I made one mistake in my life and I have immediately took responsibility for it," said Michael Daughtry, a gun store owner and former police officer who pleaded guilty to a misdemeanor charge this past March. "I apologize to the court for my indiscretion. But does a person not get to make at least one mistake in their entire life?"

The sentencing hearings just blocks away from the Capitol offer a noteworthy split-screen as lawmakers and their staff are in the midst of final preparations to put their investigation's findings on full display for the American people. Click here for more.

-ABC News' Alexander Mallin

Several police officers who defended the Capitol on Jan. 6 and widows of law enforcement members who died in the aftermath will be present at the hearing.

Among them are Erin Smith, the widow of Metropolitan Police Department officer Jeffrey Smith; Serena Liebengood, the widow of Capitol Police officer Howie Liebengood; Sandra Garza, partner of Capitol Police officer Brian Sicknick; Capitol Police officer Harry Dunn; Capitol Police Sgt. Aquilino Gonell; and Metropolitan Police Department officer Daniel Hodges.

Dunn told ABC News Congressional Correspondent Rachel Scott the hearing will be "triggering."

"I think about Jan. 6 daily and tonight we are going to find out stuff we didn't know," he said.

Garza told Scott she's preparing to painfully "relive the nightmare of the day." Her longtime partner, Officer Sicknick, suffered two strokes and died of natural causes one day after engaging with rioters.

"Everybody should watch the hearings because they need the truth of what happened that day," Garza said. "These are the facts -- it's important for them not to only hear the witnesses but see it again." She added, "There has to be some accountability, people are dead because of what happened."