Gaston County Emergency Management & Fire Services has ruled that the Dec. 28 house fire that killed Dennis Hamlin, the father of NASCAR driver Denny Hamlin, was accidental, though investigators have not determined what sparked it. In a report released after the incident, officials said the fire started in a bedroom of the two-story home and that the “cause of ignition” remained “undetermined,” Adam Gaub, a Gaston County spokesperson, said in an email Friday.

Officials said the house was located near Stanley, about 20 miles (32 kilometers) northwest of Charlotte, and that it was owned by a company that listed Denny Hamlin as its manager, according to government records. The fire scene produced catastrophic injuries for Hamlin’s parents, Dennis and Mary Lou Hamlin, who were found outside the home the evening of the fire, officials said.

Gaston County’s determination did not stop at the area of origin. The county’s fire investigation otherwise concluded that the blaze was accidental, even as it could not identify the specific ignition cause, Gaub wrote. Dennis Hamlin, who was 75, later died, while his wife survived, officials said.

Denny Hamlin previously said his father was already seriously ill last year. The NASCAR driver is a leading competitor in the sport’s top circuit, having won 60 NASCAR Cup Series races, including the Daytona 500 three times, and he co-owns the car driven by Tyler Reddick with Michael Jordan.