DES PLAINES, Ill. (WLS) -- Des Plaines fire officials said Thursday they are investigating a space heater as the cause of a fatal fire that killed a mother and her four daughters. The fire broke out at about 10:13 a.m. Wednesday in the 700-block of West Oakton Street. Officials said the fire started in the second floor near the top of the stairs, trapping the victims upstairs with no way to escape the century-old building. Neighbors said the girls' father, Juan Espinosa, was at work at the time. His brother, Horacio Espinosa, lives next door. He said it's very difficult to find words to express the sadness his family feels. He said they are grateful for support from the community, but life will never be the same.