EVERETT — No cause has been found for an apartment fire that nearly killed two toddler girls in late January.

The twin girls, Emma and Chloe, 3, were rescued in the arms of two Everett firefighters who found them hidden in their mother’s smoke-filled bedroom Jan. 29, in the first-floor unit at the Olin Fields Apartments.

Fire investigators believe the girls were the only ones in the apartment that afternoon, when the flames broke out in the three-story building off Holly Drive.

Because of their age, investigators were wary of giving great weight to their account of what happened, without solid scientific evidence to back it up, Everett Assistant Fire Marshal Steve Goforth said.

“As far as physical markers, it was really tough,” Goforth said. “Our first goal there was to put out the fire and rescue the girls.”

The fire appeared to have started by a sliding glass door. That’s the main entryway, so things were moved around in the rescue. Intense flames destroyed other evidence.

The girls’ older sister, 23, had been babysitting the twins that day. She had left, and returned to the apartment to find the fire was raging, according to firefighters. She screamed that the babies were still inside.

Capt. Nick Adsero and probationary firefighter Brent Duckworth rushed inside and found the girls in their mother’s bedroom, where the door had been shut. The girls later told their mother they shut the door because the smoke stank. That stroke of luck likely prevented the flames from spreading faster, firefighters said. The girls were covered in soot, with high carbon monoxide levels, when the fire crew carried them to the paramedics.

Both girls spent one night at Harborview Medical Center in Seattle. They had no signs of serious damage, and last month they reunited with the fire crew who saved them.

Police were investigating how long the girls were left unattended. The older sister has not been arrested or charged as of this week.

Damage to the building and contents was estimated at $700,000. Flames charred all three stories of the building.

This week fire investigators said the cause is officially undetermined. But if new evidence emerges, the case could be reopened.

Caleb Hutton: 425-339-3454; chutton@heraldnet.com. Twitter: @snocaleb.