A house in Harvest Road, Smethwick, was the scene of a serious fire on Saturday morning, with 19 firefighters called out to extinguish it. A woman, believed to be in her 30s, died after being pulled from a bedroom.
Fire investigators from West Midlands Fire Service have been trying to identify the cause of the blaze, and on Wednesday morning they said it was likely that the fire was an accident.
A statement on Twitter said: "Our investigators' work into this fire at the weekend continues.
"It appears at this stage that the fire started accidentally, in the downstairs lounge. Our thoughts remain with everyone affected by this incident."
West Midlands Police earlier said the fire was not being treated as deliberate or suspicious. Floral tributes have been left outside the property.
Taxi driver Ashmetullah Faizy raised the alarm when he saw the flames taking hold of the house as he got back from work just after 4am.
Mr Faizy, 38, said the fire became fierce enough to break the windows of the house as he was on the phone to 999.
He knocked on the door of the burning house along with the next-door neighbour before helping the couple who escaped and giving the man his trousers.
"I was on the phone with 999 and basically the fire started breaking the windows, everything," he said.
"I knocked the other doors of the neighbour because they have got kids, telling them to get out of the house.
"Basically, everybody was asleep. I was on the phone with the fire people and then they arrived.
"They arrived really quick to be fair, and I rang straight away as soon as I saw some lights in the lounge. Then the fire was getting really bad."