CHICAGO (AP) — Investigators seeking the cause of Chicago’s deadliest fire in well over a decade were searching the porch area where the blaze started for evidence of fireworks, cigarettes or other smoking materials, a fire official said Monday.

Fire department spokesman Larry Langford said children had been known to have set off fireworks from the porch of the Southwest Side apartment that caught fire before dawn on Sunday, killing six children and two adults and leaving a boy and a man in “very” critical condition. People had also used the spot to smoke cigarettes, he said.

Although investigators haven’t determined what caused the fire, they don’t think it was deliberately set and they have ruled out any problems with the building’s electrical wiring, Langford said. He also it quickly became clear that the lack of any working smoke detectors turned the fire deadly.

“Because of where it started, (on the rear porch of a rear building), if they had at least one smoke detector, they would have woken up and walked out the front door,” Langford said. “They could have grabbed everyone and made it out a stairway and outside (because) they had a clear shot at the front door.”

Investigators believe some of the kids who were killed in the fire were at the home for a sleepover, he said.

The Cook County Medical Examiner’s Office on Monday publicly identified three of the children who were killed as 3-month-old Amaya Almaraz, 10-year-old Giovanni Monarrez and 16-year-old Victor Mendoza. All three were listed as residents of the block where the fire occurred but, per office policy, their exact addresses were not listed.

Autopsies were conducted on the remains of all the victims but the office said it would not release the cause and manner of death until the fire department determines completes its investigation.

Langford said the fire is Chicago’s deadliest blaze since at least 2000 and may be its deadliest since 1993, when 19 people were killed by a fire that swept through the Paxton Hotel, a single room occupancy residential hotel.