By CBS3 Staff

PHILADELPHIA (CBS) – It’s a day after a fatal fire left a dozen people dead, and there is still an active scene in Philadelphia’s Fairmount neighborhood. Chesley Lightsey, supervisor for homicide and fatal shooting at the DA’s Office, told Eyewitness News that they believe a child may have been playing with a lighter near a Christmas tree in one of the units and the tree caught fire. These details were revealed in an application for a search warrant to go inside the unit where the fire began.

For now, the investigation is being led by the fire marshal’s office but includes support from multiple local and federal agencies.

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Due to the magnitude of this fatal fire, the fire marshal’s office requested additional resources.

The Bureau of Alcohol, Tobacco, Firearms, and Explosives called on its national response team to join the investigation. The ATF’s national response team has state-of-the-art equipment operated by personnel that specializes in fire origin.

Investigation Continues Into Cause Of Fairmount Fire That Left 12 People Dead, Including 8 Children

Also involved in this joint investigation into the converted apartment building located on the 800 block of North 23rd Street, where at least 26 people were living, is the Philadelphia Police Department and the Philadelphia Housing Authority.

Eight residents were able to escape, but at least a dozen people lost their lives, including eight children.

As the investigation continues, loved ones and residents gathered at a vigil outside of the Bache-Martin Elementary School Thursday night to remember the 12 people killed in a fast-moving house fire.

“Surprised. Because I didn’t know that it would actually be her,” a young girl said.

Sadness among even the smallest of Philadelphians.

“Shanise used to be my friend,” the girl said.

“Our family would like to thank everyone for their kindness, generosity and prayers during this horrific time,” family spokesperson Andrea Underwood said.

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The president of the Philadelphia Housing Authority was at the scene Thursday afternoon alongside City Council President Darrell Clarke and Congressmember Dwight Evans to talk about PHA’s investigation into this deadly fire.

PHA President and CEO Kelvin Jeremiah says the fire alarms and carbon monoxide detectors were fully operational after last year’s April and May inspections.

He says there were three generations in the home as the family grew over time, and called the notion to remove them absurd and against policy.

On the lease were 20 people, six for the first floor and 14 for the upper unit. There were 26 people inside at the time the blaze erupted. CBS3 has learned the victims include four women, five girls and three boys between the ages of two and 34.

The Philadelphia District Attorney’s Office supervisor for homicides and non-fatal shootings says a 5-year-old child claimed to be playing with a lighter and then set the Christmas tree on fire.

The 5-year-old was one of eight people who managed to escape.

Lightsey confirms that a warrant was filed in Common Pleas Court seeking permission for homicide investigators to search the fire-damaged units. CBS3 is told the application for the search warrant is only a legal formality.

Meanwhile, Jeremiah says he spoke to surviving families of both units and will do everything to ensure they have what they need including rehousing, which PHA has identified.

Officials say this investigation could take weeks.

Meanwhile, Lightsey says Pennsylvania state law does not allow persons under 10 to face criminal charges.

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CBS3’s Alecia Reid and Jasmine Payoute contributed to this report.