No word on cause of Philadelphia house fire that killed 12

City and federal investigators worked to determine the cause of a blaze that killed 12 people in a Philadelphia rowhome but had no immediate answers Thursday, cautioning the fire scene was complex and that it would take some time to determine what happened.

Specialists from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives took photos and entered the charred, three-story brick duplex, where the city's deadliest single blaze in more than a century took the lives of two sisters, several of their children and others early Wednesday.

"I know that we will hopefully be able to provide a specific origin and cause to this fire and to provide some answers to the loved ones and, really, to the city," said Matthew Varisco, who leads the ATF's Philadelphia branch.

The building is owned by the Philadelphia Housing Authority, the city's public housing agency and the state's biggest landlord.

Fourteen people were authorized to live in the four-bedroom upper apartment that "suffered the tragedy," according to Kelvin Jeremiah, the housing authority's president and CEO, while six people were on the lease in the lower unit.

When the family upstairs became tenants in 2011, there were six people — a grandmother, her three daughters and two of their children, Jeremiah said. He said the family grew over the next decade to add another eight children.

PHA "does not evict people because they have children," Jeremiah said.

"This was an intact family who chose to live together. We don't kick out our family members ... who might not have other suitable housing options," he said.

Jeremiah, who struggled to keep his composure at times, said the authority has reached out to the surviving family members from both units to help rehouse them.

"All of us at PHA are shaken," he said.

Fire officials provided few details at a separate news briefing, declining to say how many people escaped the blaze or speculate on a possible cause. They also did not say where the fire began, calling it part of the investigation.

The fire department previously said none of the four smoke alarms in the building, which is public housing, appeared to have been working. But housing authority officials said Thursday the building actually had 13 tamper-resistant, 10-year detectors in the units, all of which were operational during the last inspection in May 2021.

The residential block remained eerily quiet earlier Thursday, with the exception of a trash truck that rumbled down the street. Few residents were out and about.

The Philadelphia school district said counseling and support services were available for students and staff "grieving this unimaginable loss." The city's emergency management office opened up a support center for friends and relatives at an elementary school that one of the victims attended.

At least two people were hospitalized and some others managed to escape from the building, officials have said. Officials said Wednesday that 26 people were staying in the two apartments. The fire marshal, Deputy Chief Dennis Marrigan, said Thursday that investigators were seeking to determine how many people lived in the building and how many might have just been visiting.

He called the building a "very, very sophisticated scene. It's a very traumatic scene, and it's very complicated. It's a very complex investigation."

Marcia Fudge, secretary of the U.S. Department of Housing and Urban Development, expressed condolences on Twitter and said HUD had been in touch with city leaders and "stands ready to support the community in any way possible." HUD investigators were in the city on Thursday, according to Marrigan.

Officials did not release the names or ages of those killed in the blaze, which started around 6:30 a.m. Wednesday.

Family members on Facebook have identified two of the victims as sisters Rosalee McDonald, 33, and Virginia Thomas, 30. The siblings each had multiple children, but it's unclear if all of them were home at the time of the fire or how many of them died. Messages were left with several people who said they knew or were related to the victims.

Fire officials had initially said 13 people died, seven of them children, but those figures were updated Wednesday evening. The victims included eight children and four adults, officials said.