PHILADELPHIA (CBS) — There are many questions surrounding the Philadelphia Housing Authority property at the center of Wednesday’s deadly fire, from how many people lived inside the home to if the smoke detectors inside were operational. The main question: What went wrong?

Sources close to the investigation tell CBS3 all indications are the deadly fire that killed at least a dozen — including eight children and four adults — was a terrible accident.

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Neighbors and residents told CBS3 they sounded the alarm with PHA many years ago about escape routes during a fire. Regina Cureton, who lives in a PHA unit, blasted the housing authority for what she claims have long been lapses in proper safety measures — including how to get out in case of a fire.

“They gave us no fire escape, they told us to jump out the window, that was what I was told by the Philadelphia Housing Authority,” Cureton said. “And I’m very angry, I’ve been trying to contact them for two years and now that I see that these people died, I told them this, I warned them this was going to happen, and they ignored all my calls.”

Sources confirm to CBS3 the Philadelphia Fire Department is doing thermal imaging to find the placement of the victims inside.

From there, officials will look at schematics to build a picture of how the fire spread so quickly.

A joint investigation into the staggering loss of life has been initiated between the Philadelphia Police Homicide Unit, the Philadelphia Fire Department and the Bureau of Alcohol, Tobacco and Firearms.

The building, owned and subject to inspection by the Philadelphia Housing Authority, had properly working smoke and carbon monoxide detectors as recent as this spring, according to inspection reports.

CBS3 dug into the records of the home involved, which was last inspected in May 2021. At that time, there were six smoke detectors and three Carbon Monoxide detectors in Unit B. Unit A’s inspection came a month before, which revealed seven smoke detectors and three Carbon Monoxide detectors.

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But officials were quick to note no working detectors were found after the fire had been extinguished.

“So as of right now, the Fire Marshal, along with ATF, are in the process of doing a thorough investigation of this terrible event,” Deputy Fire Commissioner Craig Murphy said. “There were four smoke detectors in that building and none of them operated.”

Fire investigators spent much of Wednesday afternoon using infrared-type scanners to pinpoint where each of the victims died inside the brownstone building.

Officials with the fire department described the building’s configuration as unusual and say upwards of two dozen people were inside at the time.

A senior vice president with PHA who showed up at the fire scene was asked about the discrepancy over whether smoke detectors were working.

“I don’t know if they were replaced, tampered with, I have no idea,” Dinesh Indala said. “We’re working with the fire department at this time as part of the investigation.”

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Stay with CBS3 on-air, online and on our streaming channel CBSN Philly for the latest on this tragic event.