Sources tell Action News that, on Wednesday, workers were using torches to work on decorative balcony railings at a wood-framed building when the fire began.
However, exactly how the fire started is still unknown, and is expected to be revealed at a news conference early next week.
The two undamaged buildings have now been turned over to the control of the property manager.
Workers will spend the weekend replacing door locks broken during the evacuation and replacing 900 batteries in the smoke detectors. That means residents may be able to return home sooner than expected.
Residents of the two fire-damaged buildings returned to the scene today. Investigators say, the remains have been stabilized, and the damaged portions have been torn down.
They are not allowed inside, but those who lived in the damaged buildings will be able to submit lists of items they'd like to retrieve, and search teams will go in after them.
There are still miracles in the rubble. A dog was found in one of the building being demolished yesterday. The owner has two. One got out when firefighters opened the door. The one found yesterday hid under the bed.
"They flipped the mattress because she ran under the bed, and they couldn't get to her," said Lisa Malagloi. "They were called out of the building. I think they were afraid of it collapsing."
Action News has learned that a number of other pets have been rescued from a partially destroyed building that was being demolished.
Others have lost everything, and some of the residents have retained a lawyer to prepare a class action lawsuit and they're gathering signatures.