The alleged gunman in Wednesday's shooting spree in a village near Kingston was complaining a few days ago that he had a trapping dispute with a person who was eventually shot dead.
The tragedy, which ended with two dead men and two injured people, unfolded around Tamworth and Erinsville, two rural communities north of Napanee.
The shooter died at the end of the mayhem. While the Ontario Provincial Police was called to intervene, the man did not die as a result of a police shooting, said OPP Sergeant Kristine Rae.
The suspect's name has not been released but residents said he is a local handyman in his 50s named Morton Lewis.
The province's Special Investigations Unit has been called in to investigate. Its mandate is to examine cases involving police that result in serious injury or death.
Mr. Lewis was cornered after a rampage that involved six crime scenes, including the Tamworth post office.
A local man, described as a hermit-like figure who lived in a barn after his house burned a few years ago, was shot dead.
A firefighter was wounded and the gunman also rammed a female motorist, who was injured while she tried to jump out of the way.
Mr. Lewis leased a plot where he trapped beavers and muskrats, said an acquaintance who had a conversation with him three or four days ago.
"He told me at the time that he had an issue with trapping rights," the acquaintance said.
"He told me about somebody who lived in a barn and that he was part of what he was talking about … he mentioned this fellow who lived in a barn."
A father of two grown children, Mr. Lewis was the town's fix-it man, earning some money repairing cars, tractors and lawnmowers.
He lived in the basement of his house, renting the upper floor. He also had a small runway on his property, which he used to fly his ultralight aircraft.
"My head is still spinning because it doesn't seem like the Mort that I knew," said the acquaintance. "He seemed a pretty calm and easy-going fellow … I think about it and I can't believe it."
The acquaintance was also baffled why Mr. Lewis would have pointed a gun at Kate McDonald, who manages the Tamworth Canada Post office.
"She's very well-liked. She knows everybody and is a very cheerful person. I can't imagine anybody who would want to harm her."
The tragedy unfolded late Wednesday afternoon.
Mr. Lewis is believed to have crashed his vehicle into two garages while he was fleeing from police.
A member of Ms. McDonald's family said the suspect pointed a firearm at her and also crashed into a car driven by a young female relative of Ms. McDonald, who has been identified as Karen Cassidy.
"She broke her ankle when the guy rammed into her car. She jumped into the back because he was going to ram it again," the relative said.
The young woman was taken to hospital, first in Napanee, then Kingston.
A local firefighter, Chase Wayte, was shot in the arm near the post office, a neighbour said.
"Everyone I spoke to are shaken up. I know the family of the firefighter. They are just glad he is okay and God was watching over him," the neighbour told The Globe and Mail.
District fire chief Richard Easterbrook confirmed that a local firefighter had an injury that was not life threatening.
"No words can describe what happened today in Tamworth. I pray I never see this horrible carnage again," fire captain Tim Kidd wrote on his Facebook page at 3:20 a.m.
The OPP said there were six separate crime scenes involved in the investigation. The force gave few others details because the SIU is now involved.
Local TV station CKWS said OPP officers were stationed at the local post office, where evidence markers had been placed around cartridge casings on the ground. Officers were also monitoring the local fire station, two homes and two spots along a county road, according to CKWS.
Tamworth is a town of roughly 500 people in Eastern Ontario, north of Napanee.
With reports from Joe Friesen and Rick Cash in Toronto