(AP) - Investigators say they still can't pinpoint a specific cause in the fire that killed 36 people in an Oakland warehouse.
They focused their investigation on electrical appliances plugged into the rear of the building where the fire started.
The U.S. Bureau of Alcohol, Tobacco and Firearms said Tuesday it has finished collecting evidence. The Oakland Fire Department will prepare a final report for handover to prosecutors.
Prosecutors have warned murder charges are possible as they determine whether crimes are linked to the blaze.
The deadliest building fire in the U.S. in more than a decade erupted during a dance party Dec. 2. The warehouse had been converted into art studios and illegal living spaces.
Former denizens said it was a death trap of piled wood, furniture and electrical cords with only two exits.
Building department inspectors had not gone into the warehouse since at least 1986.