When Abbotsford Police Constable John Davidson put his life at risk to subdue a gunman who was firing at civilians, the officer was using training that can be traced back to the Columbine High School shooting of April, 1999.

Until then, police responding to active-shooter situations were trained to secure the perimeter and attempt to negotiate with the subjects while specialized teams arrived, said Sergeant Mike Massine, a use-of-force co-ordinator at the Justice Institute of B.C.

But the high-school shooting rampage revolutionized the way police officers in North America handle such situations. The priority now is to stop the shooter as soon as possible, despite the heightened risk to officers.

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Abbotsford Police Chief Bob Rich has repeatedly praised Constable Davidson's heroic actions.

"We train our police officers, we ask our police officers, that when somebody is putting people's lives in danger, when there's an active shooter, we no longer wait for cover, we no longer set up teams. The first person in goes," Chief Rich said on Tuesday, his voice filled with emotion.

"John Davidson was the first person in and he went. And he died protecting you and me."

In Columbine, the first officers to arrive at the scene secured the perimeter; a SWAT team entered the building 47 minutes after the shooting began. In all, Eric Harris and Dylan Klebold killed 13 people and wounded more than 20 others.

Soon after, the U.S. National Tactical Officers Association, which trains emergency response teams and other specialized personnel, initiated new training that has since been adopted across North America.

"There was an agreement … that if you have an incident like this, the number one priority is to get in there and stop the killing," Sgt. Massine said.

Rick Parent, a former police officer who now works as an associate professor at Simon Fraser University's school of criminology, said while the new approach placed a higher risk on officers, "the bottom line is that you're saving lives."

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The reality is that it is often officers on patrol who respond to these calls, Dr. Parent said, and waiting for an emergency response team with more specialized tools could cost lives.

"Cops really do risk their lives in these situations, but it's a good thing for society to have this immediate response," he said.

Both Dr. Parent and Sgt. Massine pointed to the September, 2006, shooting at Montreal's Dawson College as an example of how the new training saved lives. In that case, two officers who were on campus for an unrelated reason rushed toward the sound of gunfire without hesitation.

Sgt. Massine said his heart goes out to Constable Davidson's family.

"When something like this happens, especially so close to home, it takes a piece out of you," he said.

"Police officers swear an oath when we get hired, and from what I heard, I think Constable Davidson upheld his oath to the highest degree."

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Oscar Arfmann, 65, has been charged with first-degree murder in connection with Constable Davidson's death.

In a statement, Mr. Arfmann's sister-in-law said the accused "was really never the same" after his wife Patricia died in April, 2013.

The statement from the family said Mr. Arfmann was admitted to hospital in St. Paul, a town northeast of Edmonton, in July of 2015 for a mental evaluation, but he was released three days later. Mr. Arfmann's family said they wanted to extend their deepest condolences to Constable Davidson's family and the Abbotsford Police Department.

Mr. Arfmann remained in hospital on Tuesday and British Columbia's civilian agency that investigates police actions resulting in serious harm or death has said it's believed he was shot.

The statement released by Mr. Arfmann's sister-in-law on behalf of the family said Mr. Arfmann continued to struggle with mental-health issues after being released from hospital in 2015.

"Family members had tried to seek help for him but he refused to go to the doctor," the statement says.

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With a report from Mike Hager and The Canadian Press