The State Fire Marshal has ruled there was no criminal activity leading to a fatal Bridgeport fire.
Officials say their investigation is complete and the cause of the fire is currently undetermined-- but they say they can't rule out the possibility of electrical problems as the cause.
The parents were seriously injured in the fire and remain in a Pittsburgh Hospital fighting for their lives.
One day after the three small children die in an apartment building fire in Bridgeport, their parents are still fighting for their lives in a Pittsburgh hospital.
Back at the scene, investigators are literally crawling through the rubble to find the answers.
Ronald Willis of Bridgeport said he heard yelling Sunday morning in the apartment building next door.
"And it just seemed like the fire spread so quickly," Willis said. "We just had enough time to hurry up and get a few things out, and get my mother down the stairs and out the door."
He didn't know the family in the adjoining building, but he was horrified to learn that their children died.
"Oh that's a tragedy," he said. "I had no idea that was happening."
Gordie Longshaw, owner of City Advertising across the street from the fire, said the family whose three children died had only lived there about two weeks.
"No one really got to know them," said Longshaw. "The kids weren't registered at school. So there's not much background knowledge on them."
It's the topic of conversation everywhere as the state fire marshal's investigators and Bridgeport firefighters sift through the rubble to find the cause.
They say speculation is rampant, on the street and in social media.
But the only reality is that a badly burned mother and father are fighting for life in a Pittsburgh hospital, while a fund is set up for the children's funeral arrangements.
Donations are being accepted at Wilson Funeral Home in Bridgeport.
Meanwhile, debriefing teams have been helping firefighters to work through what they experienced.
"Any loss is a tragic loss," says Assistant Fire Chief Mel Roth. "And we have things in place to assist those who were involved yesterday."
Many people are feeling the loss, calling it the worst nightmare imaginable.
"The fire department showed up quickly," said Longshaw. "But for the kids to be trapped upstairs, that's sad. It's a sad day in Bridgeport."
Investigators emphasize the investigation is far from over.