NEWSTALK 1010 has learned that the fire at 235 Gosford Blvd in November, was caused by a space heater, placed too close to a mattress.
Officials from the Ontario Fire Marshal's office says the fire was accidental, but there were other factors at play.
First, the smoke detector was working in the eighth floor unit was working, but was silenced when it initially went off.
Then, officials say, the people in the unit tried fighting the fire by themselves, without calling 9-1-1.
An alarm in a common area, near the elevators on the eighth floor triggered, and the alarm company called Toronto Fire. But by that time, too much time had elapsed and the fire was heavily engrained in the apartment.
"Had that been a normal response, the fire service would have been able to respond, and been able to put that fire out, and it would have been somewhat routine," says Rick Derstroff, from the OFM, who was the lead investigator into the cause.
The damage left behind was severe, so that hampered their investigation into the two-bedroom unit.
It is worth saying though, that prior to the fire, the building had all up-to-date safety features in it. Derstroff even checked smoke detectors himself through the building to make sure they were operational.
"They were all newer smoke alarms, with fresh new batteries, so the structure itself, the apartment building, was in good condition." says Derstroff.
One person was killed when they got trapped on the balcony of unit 808, where the fire started, and officials still aren't sure why that person went that way instead of the door into the hallway.
"It wasn't a hoarder house, I mean, there was a lot of clothing and things like that stored in plastic totes, so it wasn't a hoarding issue or anything like that." says Derstroff.
What he does say is that it is important for families to develop and practice a home fire escape plan.
In addition to the one person killed, six others were hurt in the fire.
700 residents were forced from their home on that night and to this day, 29 units remain uninhabitable. Repairs are expected to take at least year.