The findings from the fire marshal came the same day as the sole surviving family member of the Dunsmuir family released a deeply personal obituary for his father, mother and two brothers.
Kevin Dunsmuir, 55, his wife Jennifer, 51, and their sons Robert, 19 and Cameron, 16, died last Friday after an early-morning fire broke out in their Howard Street home in East Gwillimbury, Ont., about 50 kilometres north of Toronto.
Another son, David, 24, is the only remaining member of the immediate family. He was away studying at Brock University in St. Catharines, Ont., at the time of the fire.
"When a family member made the 911 call the fire's conditions on the home's main floor had already blocked all avenues of escape," said fire marshal Ted Wieclawaek. "We believe the delay in fire protection played a role in this fire."
Wieclawaek said investigators' preliminary findings were that the fire originated on the main floor in the laundry room where wiring for the home's security system was located. The system provided coverage to the basement and second floor of the home, where at least one smoke alarm was located.
"The OFM has established this wiring was compromised early in the fire and this would have rendered the entire system inoperable," said Wieclawaek.
The security system wasn't "monitored," Wieclawaek said, meaning the fire department would not have been immediately notified even it the alarm had sounded.
The family members were found together in an upstairs bedroom at the front of the house.
“The people that comprised my family were larger and more impactful than could ever be described,” David Dunsmuir wrote in the obituary published in the Toronto Star.
"I have done my best, but my words cannot begin to reflect the quality of their character and their lives," he wrote.
Along with touching tributes to his parents, David Dunsmuir also wrote about his brothers. Of the youngest, Robert, he wrote: "It is unimaginable that he will no longer be a part of our lives."
Cameron Dunsmuir, meanwhile, was described as "a young man with an incredible heart. The youngest of his family, the world would have been a much better place for him to have grown in it."
A funeral for the family will be held on Friday.
The tragedy has left the small community in shock and raised questions about the local fire service. East Gwillimbury has about 80 volunteer firefighters and about six full-time staff. They're also currently in talks about possibly expanding the fire department.
It took East Gwillimbury fire crews 12 minutes to reach the Dunsmuirs' home, but by then it was fully engulfed in flames.
Addressing concerns raised in the media that fire response times were a contributing factor, Wieclawaek returned to his message of fire safety.
"As fire marshal I continue to see too many fires where the lack of functioning smoke alarms are a contributing factor in fire fatalities and serious injuries," he said.
The fire marshal confirmed to the CBC's Trevor Dunn that Central York Fire Services does have a mutual aid agreement with East Gwillimbury but that nearby Newmarket, Ont., fire crews were never called on to respond.
In the case of needing backup from Central York, Dunn said, local firefighters would only make that call after arriving on scene.
Ontario achieved its lowest number of fire fatalities last year with 67. There have been 24 reported fatalities already in 2013.
Fire investigators will now continue with forensic testing to determine the cause of the fire.