The fire that killed two boys in Middlesboro last week was an accident, authorities announced Thursday.
Ethan Barton, 12, and his brother Aaron Barton, 6, died in the fire. Their parents, Brandy Harris, 31, and Travis Barton, escaped the fire with minor injuries.
State police have not confirmed what started the fire, but they are looking at smoking or a space heater, among other things, as possible ignition sources, said Lt. P.J. Burnett.
A cigarette is the most likely cause, the state Fire Marshal's Office said Thursday in a news release.
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"We certainly don't see anything intentional about it," said Jack Flowers, an assistant state fire marshal.
It is customary in fatal fires for investigators to try to determine whether someone fell asleep while smoking or dropped burning ash from a cigarette on flammable materials.
Investigators said the fire started in the front room of the small wood-frame house, in the area of a couch.
State police were not able to locate smoke detectors in the house, Burnett said.