Children sign a Canadian flag at an impromptu memorial in front of the RCMP detachment in Enfield, Nova Scotia, Canada on April 20, 2020. (Photo: Agencies)

MONTREAL－Investigators on Monday scoured crime scenes from the worst mass shooting in Canadian history to try to understand why a dental worker with no criminal past killed at least 18 people.

The gunman, identified by police as 51-year-old Gabriel Wortman, began his rampage late on Saturday in the seaside village of Portapique, Nova Scotia, dying 14 hours later in a hail of police gunfire outside Halifax, 100 kilometers away.

"Just how could this happen, we may never know why," Canadian Prime Minister Justin Trudeau told a news conference.

"But we do know this: No one man's action can build a wall between us and a better day, no matter how evil, how thoughtless, or how destructive."

The death toll, initially put at 16, rose to 18 on Monday, Trudeau said, with police warning that more bodies could be found in the rubble of five burned out homes and buildings.

"We expect there to be more victims," said Chris Leather, chief superintendent of the Royal Canadian Mounted Police.

Among the victims so far identified were a veteran constable with the RCMP, a nurse, an elementary school teacher, prison guards and a retired firefighter.

"This happened in small towns－in Portapique, Truro, Milford and Enfield－places where people have deep roots, places where people know their neighbors and look out for one another," Trudeau said.

A "virtual vigil" has been planned for Friday.

Nova Scotia Premier Stephen McNeil said the investigation and the grieving process would be "complicated" by the coronavirus pandemic－and the vast geographic area of the crime spree.

Forensic investigators fanned out to 16 "chaotic" crime scenes across the province that is home to Canada's Atlantic navy fleet.

Some victims were not known to the shooter, while others were specifically targeted, said Leather.

"It's too early to tell what the motivation was," he said. "It appears to be, at least in part, very random in nature."

German Chancellor Angela Merkel led international expressions of sympathy, telling Trudeau in a note: "This senseless and cruel act has shaken us all deeply."

After the first gunshots rang out in Portapique, where Wortman owned two properties, police found casualties inside and outside a home and also responded to a series of blazes.

Neighbors told local media that Wortman set fire to homes and shot residents as they ran out.

An acquaintance said Wortman drove to his house in a mock squad car, wearing a police uniform, and banged on the door clutching a rifle and a pistol.

"He wasn't killing enemies, he was killing his friends," said the man, who hid with his wife and called the police. "He was trying to beat down our door. It was beyond terrifying."

Police said Wortman, still posing as a policeman, later stopped a vehicle near Debert and shot the occupants.

"A monster murdered my mother today," Darcy Dobson wrote in a Facebook post about victim Heather O'Brien, a nurse in Truro.

Agencies Via Xinhua