The man accused of killing a police officer in Abbotsford, B.C., hadn't been licensed to own a firearm for more than two years, underscoring the challenge police departments face in collecting guns from thousands of expired licensees, including those with mental-health problems.

At a news conference last week, homicide investigators said Oscar Arfmann, the 65-year-old charged with the first-degree murder of Constable John Davidson, once had a valid firearms licence, but it expired in 2015 – the year his family says his deteriorating mental health sent him to the hospital.

Mr. Arfmann's birth date is in January, which is when his five-year licence would have come up for renewal. In July of 2015, Mr. Arfmann's mental-health problems led to him being admitted to a hospital in St. Paul, a town northeast of Edmonton, for three days, according to a recent media statement from his sister-in-law. A month later, Mr. Arfmann was charged with impaired driving. Soon, the usually quiet man became known as someone to avoid, according to Brittany Plamondon, a clerk at the local grocery store and post office in the rural hamlet of Ashmont, where Mr. Arfmann lived until last year.

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Ninety days after any gun licence expires, local police are notified by the RCMP's Canadian Firearms Program, at which point officers are supposed to follow up and see what the person is doing with the weapon.

But in many jurisdictions police don't have the resources to knock on the doors of those whose licences expire each year, said Paul Ballard, who retired from a 35-year career with the Vancouver Police Department to become a master firearms instructor. An average of 88,000 Canadians had their gun licences expire in each of the last five years, according to official data.

"Every single day, somewhere in Canada, an agency is being notified that there's another person who's let their licence expire and there really isn't anything done about it," said Mr. Ballard, who trained officers in firearms for more than a decade at the Vancouver Police Department.

"Typically, for years, the Vancouver police were just overwhelmed with everything else that was going on and it wasn't exactly something they made a priority of.

"Usually what they would do is just phone the individual and tell them 'Get back on track, get your licence renewed.'"

Mr. Arfmann was an avid hunter with several firearms, according to his former sister-in-law Donna Gagnon.

The St. Paul RCMP detachment would not comment on whether the detachment's officers approached Mr. Arfmann once his licence expired or whether Mounties there proactively seize firearms from such owners. Detachment spokesperson Corporal Ron Bumbry said the Mounties do periodic drives to collect guns from owners who no longer have valid licences, but did not say how often these occur.

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If Mr. Arfmann had been licensed when he went to the St. Paul hospital in 2015, that might have flagged his licence to be suspended and reviewed by the Canadian Firearms Program, said Mr. Ballard. Last year, 2,223 people had their gun licences revoked, 424 of them for reasons that included mental health problems, according to the program's last annual report.

If friends or family feel a gun owner's mental health could lead to trouble, they have a duty to call the national firearms program or their local police force – whether the person is licensed or not, Mr. Ballard cautioned.

"It's up to you to do the right thing and tell somebody," he said.

Nick Wong, an outreach co-ordinator for Silvercore, a firearms training company in Delta, B.C., said that Canada does a great job of screening aspiring gun owners but agreed with Mr. Ballard that more could be done to monitor those who let their licences lapse.

British Columbia's civilian agency that investigates police use of force resulting in serious harm or death said it is believed Mr. Arfmann was shot last Monday during his arrest. The agency's update on Tuesday said he remained in hospital.

With reports from Wendy Stueck and The Canadian Press