One year ago today, a lone gunman fatally shot Cpl. Nathan Cirillo on the steps of the National War Memorial before storming Parliament's Centre Block building. Parliamentarians who were there that day shared with CTV News what they remember from the attack.

Conservative MP Lisa Raitt

Conservative MP Lisa Raitt said she was sitting in caucus with her colleagues when they suddenly heard a loud "bang."

At first, she thought it was related to some of the ongoing construction that was taking place throughout Parliament.

"Then all of a sudden all you heard was gunfire," she told CTV's Canada AM on Thursday morning. "Everybody ran for either a door, or you try to find a place to take cover. Because at that point in time, we didn't know if the flurry of gunfire were the good guys or the bad guys."

Raitt said once she realized that the sounds she was hearing were the sounds of gunfire, her thoughts immediately went to her two sons.

"In that moment what I was thinking was, 'Well, if this is it, I feel bad that my kids are going to have to see this on television,'" she said. "I really did think of my kids, that's what I thought of first and foremost."

Raitt said she's taking time today to reflect on the life of Cirillo, who died in the attack.

Conservative MP Tony Clement

Conservative MP Tony Clement said he remembers the chaos that broke out as the shots rang out in the halls of Parliament.

"Of course we were in a chaotic situation, so you had all sorts of emotions because you didn't know what was really happening. We didn't know if there was one shooter or multiple shooters," he said.

He added that the stonework inside Parliament's halls produced a very loud echo whenever a shot was fired.

"It sounded like there was really a team of terrorists about to break down a door and spray us with bullets. That was my first reaction. That's something you never forget," he said.

"Until that chaos cleared, you're obviously just trying to deal with your emotions and try and get through the day."

Clement later attended the funeral for Cirillo in Hamilton, Ont., along with other parliamentarians.

He remembers seeing the outpouring of sympathy from Hamilton residents, as Canadians paid respects to the fallen soldier.

"Every street was lined with people, that's one of the things I remember," Clement said, noting that he grew up in Hamilton.

"It was a very emotional moment for all of us to see. Cpl. Cirillo's family is from there, and it was a whole range of emotions."

Canadians gathered at the National war Memorial on Thursday to mark the sombre anniversary of the attack, and to honour the life of Cirillo.

The ceremony will also pay respects to Warrant Officer Patrice Vincent, who died two days before the attack in Ottawa. Vincent was run down in Saint Jean sur Richelieu, Que., by Martin Couture-Rouleau, a radicalized man who had been on the RCMP's radar.