"I guarantee the family would have got out alive if they'd just had one working smoke alarm," said Steve Henrichson, an inspector with the St. Joseph Fire Department.

Fire Department investigators were searching for a cause for the slow-burning fire that was reported at 5:32 a.m. and was largely contained on the first floor. Henrichson said it appeared to have started in a first-floor room, near an electrical outlet where a window air conditioning unit was plugged in.

All six victims were found on the second floor, said Capt. Kevin Castle, a spokesman for the St. Joseph Police Department. Neighbors said they had lived at the two-story house for about a year and a half.

Emergency personnel said they thought the oldest boy, the mother's child from a prior marriage, had also died in the fire, until he arrived at the charred house at about 9 a.m.

A fire department chaplain drove the boy to Heartland Regional Medical Center to be with family members.