A crowd of about 2,000 people — including hundreds of soldiers, government officials and citizens — gathered at the National War Memorial in downtown Ottawa on Thursday to honour the two soldiers killed on their home soil last year, and to pay tribute to the families still adjusting to life without them and the first responders who stepped in to help.

"It's been one year. We continue to grieve, we continue to heal," said Gov. Gen. David Johnston in his speech to mark "a painful anniversary."

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Cpl. Nathan Cirillo, left, and Warrant Officer Patrice Vincent, right, were killed in unrelated attacks within days of each other in October 2014. A ceremony to mark a year since their deaths was held at the National War Memorial in Ottawa Thursday morning. (Canadian Press)

The killing of 24-year-old Cpl. Nathan Cirillo at the memorial on Oct. 22, 2014, and the sounds and images of gunfire ringing through the halls of Centre Block as security staff and frightened parliamentarians raced through corridors, climbed out of windows and locked themselves in meeting rooms to escape the gunman, shocked the country and received media coverage worldwide.

Just two days earlier, 53-year-old Warrant Officer Patrice Vincent was struck and killed in a targeted but unrelated hit and run in Saint-Jean-sur-Richelieu, Que.

"We remember them, and we honour their service to Canada," Johnston said. "Their duty was to defend us and to bravely stand on guard for their country. Ours is to remember their sacrifice, and to remember why they served."

Plaque unveiled

Cirillo's mother, Kathy Cirillo, clutched her grandson, Marcus, flanked by the slain corporal's stepfather, two sisters and other relatives. Vincent's mother, Thérèse Guérette, sat next to Vincent's three sisters.

Next to the families, outgoing Prime Minister Stephen Harper and prime minister-designate Justin Trudeau sat side by side with their wives, rising together to lay a wreath at the foot of the memorial.

As they sat back down, the two leaders shook hands.

Hill Shooting Commemoration

From right: Prime Minister Stephen Harper and his wife, Laureen Harper, and Justin Trudeau, prime minister-designate of Canada, and his wife, Sophie Grégoire-Trudeau, stood side by side at the ceremony. (Adrian Wyld/Canadian Press)

A bugler sounded the Last Post, The Rouse and The Lament through an otherwise silent memorial plaza, and two minutes of silence were observed.

Four CF-18 Hornet fighter jets flew past in missing man formation — one jet moving away from the others to signify lives lost.

Johnston laid a wreath as well, accompanied by Cpl. Brandon Stevenson, the ceremonial guard who was standing sentry next to Cirillo the morning he was killed.

Master Cpl. Kyle Button, who was also part of the ceremonial guard that day and was the first to give medical care to Cirillo, accompanied Ottawa Mayor Jim Watson.

After the public proceedings were over, a plaque to commemorate Cirillo's life was unveiled in a private ceremony at the southeast side of the memorial site. A plaque to commemorate Vincent is expected to be unveiled in Saint-Jean-sur-Richelieu in 2016.

"The ceremony was absolutely beautiful. It was very impressive ... special, it was dignified," said Louise Vincent, one of the slain warrant officer's sisters, adding that the fly-by of the fighter jets was especially moving. Helicopters flew in the same formation at her brother's funeral service.

"That's difficult, because obviously it's him leaving," she said.

Dozens of lives changed

Dozens of lives were changed in the few minutes that elapsed between the first shot fired by gunman Michael Zehaf-Bibeau in Ottawa and the last that killed him, and the effects of the crime on the nation's capital are still being felt today.

It began at 9:50 a.m. on Oct. 22, 2014, a Wednesday morning.

A troubled 32-year-old Zehaf-Bibeau had minutes earlier recorded a short video manifesto on a cellphone, then used a rifle to shoot Cirillo, a reservist from Hamilton, who was serving with the Argyll and Sutherland Highlanders of Canada regiment.

Cirillo was one of two ceremonial guards — unarmed in keeping with their mandate — watching over the National War Memorial that day.

Next to the Tomb of the Unknown Soldier, a group of six people who were nearby tried to keep Cirillo alive. Lawyer Barbara Winters was one of them.

While the others performed CPR and put pressure on his wounds, Winters spoke to Cirillo.

"I told him he was loved, and that he was brave, and that he was a good man," Winters told CBC News.

"Your military family loves you," she remembered telling him. "Look at these people, we're all here helping you. We're all trying to do what we can for you. We all love you."

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Last October, police ran through the streets with their weapons drawn shortly after the shooting to establish a security perimeter downtown as investigators tried to determine if there were any other gunmen. (Sean Kilpatrick/Canadian Press)

Cirillo was taken to hospital but died of his injuries.

As the group of six — who still meet, connected even now by that day's ordeal — tried to save Cirillo's life, a still armed Zehaf-Bibeau drove to Parliament Hill, commandeered another vehicle and ran inside Centre Block.

After a standoff with security staff in the Hall of Honour, outside the Library of Parliament, Zehaf-Bibeau was shot 31 times and died.

Then sergeant-at-arms Kevin Vickers, now Canada's ambassador to Ireland, and RCMP Const. Curtis Barrett fired the fatal shots.

It was over within five minutes.

Confusion reigned for hours

While the attack took just minutes to unfold and the lone gunman was killed, confusion reigned for hours in downtown Ottawa as police worked to determine whether anyone else was involved.

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People within the downtown Ottawa security perimeter were told to leave hours after the shooting took place. The perimeter was lifted 10 hours after the shooter was gunned down. (Blair Gable/Reuters)

Thousands of workers were told to stay inside their buildings as hundreds of Ottawa police, RCMP and other officers responded, fanning out on downtown streets with their handguns and assault rifles at the ready to establish a security perimeter.

At an afternoon news conference more than four hours later, police still weren't able to say whether there were any other shooters or suspects at large.

The downtown security perimeter was lifted that night, more than 10 hours after Cirillo was gunned down, but with still no confirmation about any other suspects, Ottawans went to sleep unsure if the threat had been eliminated.

Hill security forces unified

Today, security efforts on Parliament Hill and at the National War Memorial have changed.

At the memorial, where the unarmed Cirillo was shot three times in the back, ceremonial guards remain unarmed on duty but are now closely watched by pairs of armed Ottawa police officers working in shifts, paid for by the Department of National Defence.

As for Parliament Hill security, OPP, RCMP and Ottawa police reports on the law enforcement response to the shooting all identified a need for improvement after the confusion experienced that day, created in part by the sheer scale of the response and the fact that Hill security at the time was the responsibility of three separate bodies: the RCMP and House of Commons and Senate forces.

A newly created Parliamentary Protective Service officially took control of security throughout the parliamentary precinct in June of this year. It's directed by RCMP Chief Supt. Michael Duheme, reports to the RCMP's national division and is accountable to the Speakers of the House of Commons and the Senate.

'We're always at risk now'

But while the Hill security changes are good they're not enough, according to Senator Vern White, Ottawa's former chief of police.

His main point of contention is pedestrian access to the Parliament Hill lawn. He says the entry points to the lawn should be reduced from five to three with officers stationed at each point, not to conduct searches but to talk to people about the reasons for their visits and about what's inside any backpacks they're carrying.

"I think there is a naiveté on the Hill as to the real potential for something bad to happen and how quick it could happen," White said in an interview this week.

"You go through more of a security protocol getting in to watch the Senators play hockey than you do to walk up onto Parliament Hill."

People inside Centre Block were fortunate there was only one person with one weapon and not much of a plan involved in the Oct. 22 attack, White said.

"I think if it had been more than one … it would have been much more tragic and much more difficult for us to get past," he said.

"This is a bit of our new normal. I'm not going to suggest what will happen tomorrow, but I do think we're always at risk now."