PLATTSBURGH, N.Y. (AP) — State police upstate New York say a 55-year-old Essex County man suffered a heart attack before the tractor trailer he was driving veered off the roadway and crashed into trees.

Troopers say Stacey Mitchell, of Port Kent, was hauling asphalt Wednesday afternoon when his truck veered off Interstate 87, the Adirondack Northway, in the town of Plattsburgh. Responding officers say they found Mitchell unconscious at the scene and performed first aid.

Mitchell was then transported to a hospital where he was pronounced dead.

State police say the investigation is continuing, and it was unclear what caused the truck to go off the road.

Troopers say Thursday that an autopsy conducted at Champlain Valley Physician's Hospital in Plattsburgh determined the cause of death to be a heart attack.