OXFORD – Investigators have declared that the trailer fire at Oxford Pines Trailer Park on Tuesday that killed a 7-year-old boy was accidental.

State Fire Marshal’s Office investigators said it appeared the boy’s father, Neil Gephart, had fallen asleep while smoking shortly before flames consumed the trailer.

“He had fallen asleep while smoking a cigarette on the couch before going to bed,” said Maine Department of Public Safety spokesman Stephen McCausland. Shortly after Gephart went to bed, fire ripped through the living room and spread to other parts of the trailer on Cheryl Lane.

Investigators determined the blaze began around the living room couch.

Gephart and his wife, Kathy Bennett, were treated for cuts and smoke inhalation.

Their son, Shawn Bennett, 7, and 11-month-old daughter, Andrea Bennett, were rescued from the burning trailer – one by a neighbor, the other by a police officer – but Shawn Bennett later died at a Norway hospital.

Andrea was listed in fair condition Thursday at Maine Medical Center in Portland, a spokesman said. Her condition had improved from critical.

After determining the cause, fire investigators asked state police to assist with the probe as they continue looking into other aspects of the the fatal blaze.

“There are some other questions that need to be answered,” McCausland said. “We have assigned a detective to help with that.”

Police and fire officials will continue to investigate conditions at the Bennett home before fire destroyed the trailer. McCausland said details about that phase of the investigation were not being disclosed.