Nova Scotia shooting may have begun as a domestic violence dispute: Investigators

At least 22 people were killed in the spree.

Investigators say this weekend's mass shooting in Nova Scotia, which has left at least 22 dead, marking the worst shooting in Canadian history, may have started as a domestic violence dispute.

Canadian law enforcement officials said 51-year-old Gabriel Wortman allegedly targeted his former partner during the killing spree which took place at six sites and destroyed several properties. Investigators said some of the other victims, including Royal Canadian Mounted Police Constable Heidi Stevenson, were randomly killed.

Wortman allegedly burned down his own home Saturday and made his way to his ex-partner's residence, killing other people who lived there, according to law enforcement officials. Dead bodies were also found near the former partner's home, investigators said.

When officers arrived, a "chaotic scene" ensued, and Constable Stevenson, a 23-year veteran of the force, was killed while responding, Royal Canadian Mounted Police Chief Superintendent Chris Leather said.

Five properties allegedly were set on fire by Wortman, and more victims were believed to be in homes that "burned to the ground," Leather said Monday. A 17-year-old was among the victims but everyone else was an adult, police said.

It was unclear if Wortman's ex-partner was among the casualties, investigators said.

Officers caught up to Wortman at a gas station 57 miles south of Portapique Sunday morning where he was shot and killed. As of Wednesday, 22 people were killed in the entire incident and it's unclear if the toll will rise, according to officials.

"That part of the investigation is still very much ongoing, and again, speaks to why we don't have a final total because we expect that to rise in the coming days," Leather said Monday.

Wortman was wearing what appeared to be a police uniform and drove a vehicle made to appear like a police cruiser, which helped him move around the province undetected, Leather said. Wortman was not employed by the RCMP, police said.

Investigators said the "complexity of the tactics involved in this incident—specifically the impersonation of law enforcement with both a vehicle and a uniform, the use of fire as an additional weapon during the shooting, and the high number of fatalities"— would suggest premeditation.

In a statement, Prime Minister Justin Trudeau said he was "saddened to learn about the senseless violence in Nova Scotia."

"As a country, in moments like these, we come together to support one another. Together we will mourn with the families of the victims, and help them get through this difficult time."

Queen Elizabeth also sent her best wishes on Tuesday, writing, "Prince Philip and I have been deeply saddened by the appalling events in Nova Scotia, and we send our condolences to the families, friends and colleagues of those who have lost their lives."

ABC News' Josh Margolin and Christine Theodorou contributed to this report