PHILADELPHIA (CBS) — Federal authorities are assisting in the investigating into a fire over the weekend in North Philadelphia that claimed the life of a firefighter and a civilian.

Pennsylvania Governor Tom Wolf has ordered all state flags be lowered to half-staff in honor of Lieutenant Matt LeTourneau. Monday would have mark the fallen hero’s 11th anniversary with the Philadelphia Fire Department. Instead, ATF agents are assisting the city’s fire marshal with their investigation into what happened Saturday morning when LeTourneau became trapped inside a home on Colorado Street.

Special Agent Charlene Hennessy says the house is not yet stable for investigators to go inside.

“First we need to make sure the structure is secure so the investigators can get in there to try to determine the origin and cause,” she said. “We have all kinds of hazards that these responders come across that are still there when the scene is safe.”

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She says the weather is slowing down the process, but once the structure is secure, the task force will digitally map the entire building.

“It is used to create a digital blueprint of the structure and to document the damage caused by the fire. It’s a more efficient way to preserve an exact imprint of the scene,” Hennessy explained. “It’s similar to taking photos and sketches, but this is now digital and they are able to produce digital scene diagrams and drawings and collect data for modeling for the future origin and cause determination.”

She says there is no reason to believe the blaze was arson, but she says they will also bring in accelerant-sniffing dogs to rule it out.

Hennessy says investigations have no timeline – and it could be weeks, months or even longer before they find out what happened.