(WASHINGTON) -- Two years after the Jan. 6 attack, U.S. Capitol Police officer Harry Dunn says he's still dealing with the emotional scars from that day.
Dunn, who struggled to defend the Capitol amid the hours of violence, described how his PTSD flared up this past fall.
"That moment in time hit me so hard is because I have made such good progress, to heal and be able to deal with these emotions and these feelings in a healthy manner and, you know, I could walk in and not be fazed by seeing somebody in a MAGA hat or a Confederate flag …. I made such good progress," Dunn said in an interview with ABC News Chief Justice Correspondent Pierre Thomas.
"But it was all just like out of nowhere just ripped away from me. And it wasn't a specific incident that caused it. Man, I thought I had this under control. I beat this," he said. "But no, it literally just came out of nowhere and it broke me, you know it broke me."
The interview will air on ABC's This Week with George Stephanopoulos on Sunday.
Nearly 140 officers from both the Washington's Metropolitan Police Department and the Capitol Police were injured when pro-Trump rioters stormed the Capitol, according to a recent estimate by the U.S. Capitol Police union.
While Dunn said he has more good days than bad, he said the insurrection is never far from his mind. He continues to work at the Capitol, making a point of walking through the Rotunda each day, marveling at all it means to him and the country, mindful that all it stood for could have been toppled two years ago.
On Friday, Dunn and fellow officers will be awarded the Presidential Citizens Medal -- the nation's second-highest civilian honor -- from President Joe Biden.
Dunn, who testified before the House Jan. 6 committee, told Thomas that Donald Trump needs to be held responsible.
"I believe he should be held accountable for his actions or inactions of that day. … And he needs to be held accountable and that's why all eyes are on the Justice Department right now," he said. "Because they're the ones who can bring forth accountability. … There were criminal things that the former president has done. I don't see how you cannot hold him accountable for that day," he said.
ABC News' Ely Brown contributed to this report.