Before blazing a trail of carnage across Nova Scotia, the man behind one of Canada's worst mass killings attacked his longtime girlfriend -- a story domestic violence experts say is eerily familiar.

Police say this assault was potentially the "catalyst" for the horrific murder spree that claimed 22 victims last week.

Many mass killings begin with abuse of the people closest to home, say researchers and advocates. To prevent future tragedy, they say authorities need to recognize the threat domestic violence poses to the public.

"When women are in danger in our community, all men, women and children are in danger," said Peter Jaffe, a psychologist who has studied violence against women and children for 40 years.

"It's not just an issue of violence against women. It usually suggests a much broader pattern of concern about the perpetrator."

The Western University professor co-authored a study for the Canadian Domestic Homicide Prevention Initiative that analysed 418 cases of domestic homicide in Canada between 2010 and 2015. Researchers found 13 per cent of cases involved the homicide of third parties, including family members, new partners and bystanders.

A recent report by American non-profit Everytown for Gun Safety also indicates that in more than half of U.S. mass shootings between 2009 and 2018, the perpetrator shot a current or former intimate partner or family member.

Some of Canada's deadliest mass murders fit that pattern, said Jaffe.

In Edmonton, a man suspected of domestic violence shot and killed six adults and two young children before killing himself in 2014, marking the worst mass shooting in the city's history.

In 1996, a man enraged by his wife's divorce action killed her and eight of her family members then shot himself in Vernon, B.C.

Jaffe noted that the gunman who killed 14 women at Montreal's Ecole Polytechnique in 1989 had experienced violence in the home as a child. This suggests the cycle of abuse can have far-reaching -- and sometimes fatal -- consequences across generations, he said.

In many cases, Jaffe said, law enforcement or community members are aware of a perpetrator's domestic abuse before the broader bloodshed begins.

He said reports indicate that may have been the case for 51-year-old Gabriel Wortman and his longtime girlfriend. But it's unclear whether anyone tried to intervene before the domestic assault that set him off on a shooting and arson spree across Nova Scotia last week.

One neighbour in the coastal town of Portapique said Wortman was openly controlling and jealous of his partner, but he never saw the couple's fights come to blows.

At some point last Saturday night, the woman was beaten and allegedly bound, according to sources who spoke on the condition of anonymity. Police said the woman managed to escape their home and hid in the woods overnight. When she emerged at daybreak, she called 911 and provided authorities information about the suspect.

Meanwhile, the gunman was passing through rural communities disguised as an RCMP officer, shooting people and setting houses ablaze. After a 13-hour manhunt, he was fatally shot by police Sunday at a gas station in Enfield, about 90 kilometres south of Portapique.

Julie Lalonde, an Ottawa-based women's rights advocate, said victims of domestic violence often stay with their abusers because they're scared that leaving could put others at risk.

Lalonde is concerned police are reinforcing those worst fears by framing the killer's attack on his girlfriend as the potential "catalyst" for the slayings.

She believes RCMP never intended to "blame the woman." In fact, they've called the woman a "key witness" in their investigation.

But Lalonde said these beliefs are so insidious they're embedded in our language about domestic abuse.

She said society looks down on women who stay with their abusers, then holds victims who fight back responsible for other casualities of the violence they've suffered behind closed doors.

"(This woman) has to live in a world in which this messaging is out there that maybe if she hadn't resisted, that she would have been the only one killed that night."

More than 99,000 Canadians aged 15 to 89 were victims of intimate partner violence in 2018, representing nearly a third of violent crimes reported to police, according to Statistics Canada.

The agency also recorded 945 intimate partner homicides between 2008 and 2018, nearly 80 per cent involving female victims.

Kaitlin Geiger-Bardswich, communications and development manager for Women's Shelters Canada, said the role of gender in mass shootings often isn't talked about, even though misogyny seems to have been a motivator in two of the deadliest massacres in Canada's history.

Marc Lepine, the perpetrator of the Polytechnique killings, said he was "fighting against feminists" he blamed for his troubles.

Alek Minassian told police he drove a van along a crowded Toronto sidewalk, killing 10 people and injuring 16 others, in retribution for years of sexual rejection and ridicule by women. The overseeing the first-degree murder trial said the case will turn on his state of mind at the time of the attack, not whether he did it.

There's no evidence that Lepine or Minassian had a histories of domestic violence, nor have police indicated that last weekend's killings were fuelled by sexism.

Geiger-Bardswich acknowledgeds that there's a difference between hurting individual women and hating women writ large.

But she said domestic abuse and misogyny-driven murder are part of the spectrum of violence against women that puts everyone at risk.

"If we address domestic violence and violence against women as a whole, we can better stop the killings that target men and women."

For that to happen, authorities must take robust action to address domestic violence, said Nancy Ross, an assistant professor at Dalhousie University's school of social work.

Ross said this need has become more pressing as police forces and women's shelters have seen a surge in domestic violence reports since COVID-19 forced victims to stay home with their abusers.

Canada's approach to domestic abuse has been defined by a lack of resources and fragmentation, said Ross. It shouldn't take a mass murder and pandemic to change that, she said, but the issue can no longer stay in the shadows.

"This interpersonal violence, all forms of it thrives in silence," said Ross. "If anything, this mass shooting insists upon further resources and attention."

This report by The Canadian Press was first published April 26, 2020.