Prosecutors say murder charges are possible after a warehouse fire killed at least 36 people in Oakland, California.
Alameda County district attorney Nancy O'Malley said her office has just started its probe and has not yet determined whether a crime occurred, but charges could range from murder to involuntary manslaughter.
Investigators with the district attorney's office are making sure crews removing debris do not jeopardise any evidence in a potential criminal investigation.
The fire erupted during a dance party late on Friday night. It is still unclear how it started.
Hundreds of family members and friends face an agonising wait as firefighters continue the painstaking search for victims.
The laborious job of digging with shovels and buckets through the debris was suspended overnight because of a dangerously unstable wall.
The cluttered warehouse had been converted to artists' studios and illegal living spaces, and former residents said it was a death trap of piled wood, furniture, snaking electrical cords and only two exits.
Ms O'Malley said. "We just started our investigation, and we owe it to the community and those who perished in this fire, and those who survived the fire, to be methodical, to be thorough, and to take the amount of time it takes to be able to look at every piece of potential evidence."
Oakland city councillor Noel Gallo, who lives a block from the warehouse, said he confronted the property's manager - Derick Ion Almena - several times about neighbours' concerns over rubbish in the street and in front of the warehouse.
Mr Gallo said Mr Almena essentially told authorities to "mind their own business" and appeared resistant to addressing complaints and complying with city codes.
Mr Almena and his partner Micah Allison ran the building's arts colony, called the Satya Yuga collective. They were believed to have been away at the time of the blaze.
The warehouse is owned by Chor N Ng, her daughter Eva Ng told the Los Angeles Times. She said the warehouse was leased as studio space for an art collective and was not being used as a dwelling.
"We are also trying to figure out what's going on like everybody else," the family wrote in a statement to NBC Bay Area. "Our condolences go out to the families and friends of those injured and those who lost their lives."
Questions persisted about whether city officials could have done more to prevent the fire. Oakland planning officials opened an investigation last month after repeated complaints about the warehouse. An inspector who went to the premises could not get inside, said Darin Ranelletti, of Oakland Planning Department.
Oakland mayor Libby Schaaf said city officials are putting together a record of what they knew about the property.
Investigators said they believe they have located the section of the building where the fire started, but the cause remains unknown.