Closing out the first hearing of the select committee, Chairman Rep. Bennie Thompson asked the witnesses what they expect this committee to do as it begins its work.

All four officers shared the sentiment that they want an investigation into those in power who may have aided and abetted rioters. 

"In the academy, we learn about time, place and circumstance in investigating potential crimes and those who may have committed them," said Metropolitan Police officer Michael Fanone. "So the time, the place and the circumstances of that rally, that rhetoric and those events, to me, leads in the direction of our president and other members, not only of Congress."

Metropolitan Police Department officer Daniel Hodges said his colleague hit the nail on the head, adding, "I need you guys to address if anyone in power had a role in this."

Capitol Police officer Harry Dunn used an analogy with a hitman to describe his expectations for the committee.

"If a hitman is hired and he kills somebody, the hitman goes to jail, but not only does the hitman go to jail but the person who hired them does. There was an attack carried out on Jan. 6 and a hitman sent them," he said. "I want you to get to the bottom of that."

Metropolitan Police Department officer Daniel Hodges, who referred to the pro-Trump mob as "terrorists" or "terrorism" at least 15 times in his opening testimony, defended using the term. 

"Why do you call the attackers terrorists? And what do you think of our colleagues who call them tourists?" asked Rep. Jamie Raskin, D-Md., referring to a comment by a GOP Rep. Andrew Clyde of Georgia referring to the scenes of rioters as looking like a "normal tourist visit."

"Well, if that's what American tourists are like, I can see why foreign countries don't like American tourists," Hodges said to laughter in the room.

“But I can see why someone would take issue with the title of terrorist," he continued. "It's gained a lot of notoriety in our vocabulary in the last couple of decades. We like to think that couldn't happen here. No domestic terrorism, no homegrown threats but I came prepared."

He then recited the U.S. code defining domestic terrorism as "activities that involve acts dangerous to human life that are a violation of the criminal laws in the United States or any state. And B, to be intended too, intimidate or course a civilian population or influence policies by intimidation or coercion or to effect the conduct of a government by mass destruction, assassination or kidnapping," Hodges read.

All over Capitol Hill, reporters have noticed that Capitol Police officers are intently watching the hearing -- as the four officers who are testifying Tuesday speak for many. 

Groups of police are huddled around televisions that are stationed next to security checkpoints. Some officers have been spotted watching the hearing on their phones.

Officers were seen in the Cannon Office Building standing and watching a TV screen, with the volume on high, completely engrossed as their colleagues speak their truth of what happened that day.

-ABC News' Mariam Khan