DENVER -- Investigators are trying to figure out what sparked a house fire that killed an elderly woman in Lakewood Saturday morning.

A neighbor told 7NEWS that he smelled smoke in his own basement then ran upstairs to see if his house was on fire.

"I didn't see anything, so I went outside and there was smoke pouring from the house next door," said Shane Marquardt.

At first, Marquardt thought he might be able to extinguish the fire.

"But then I saw (embers) flying in the air, so I ran back into my house to get my cell phone," he said.

Smoke and flames were coming from the home at 1310 S. Pierce St. when firefighters arrived at 2:50 a.m., said West Metro Fire spokeswoman Michelle French.

As firefighters were putting out the fire, they found the woman dead inside, French said.

Investigators had to wait until morning before they could begin looking for the cause of the fire.

"The water froze on the street," French said. "It did prove treacherous for our firefighters."

Neighbors identified the victim as 84-year-old Sally Over.

"She was a good neighbor," said Janella Reichel, a single mom who moved next door to the Overs 28 years ago.

"When I moved in, she and her husband George automatically took the kids under their wings. They were like grandparents," Reichel said.

Sally Over had lived alone in the house since her husband died in 2000.

Investigators are still trying to determine what caused the fire.

"It does not appear to have been intentionally set," French said.

Reichel said she heard that it may have been a space heater.

"It's just sad how she died," Reichel added. "I wish she would have let us spend more time with her, but she became a bit of a recluse after George passed away and after their two dogs died."