Macclesfield, N.C. — A 13-year-old Edgecombe County boy who was left tied to a tree for 18 hours last June died of dehydration and heat stroke, according to an autopsy report released Monday.

Tyler McMillan's parent found him unresponsive on June 12 after he had been left tied to a tree overnight as punishment, authorities said. He was pronounced dead at Heritage Hospital.

Prosecutors have charged his father and stepmother, Brice Brian McMillan, 41, and Sandra Elizabeth McMillan, 36, both of 1110 Felton Farm Road in Macclesfield, with murder and felony child abuse.

Brice McMillan told deputies that he twice tied his son to a tree as punishment for disobedience and that the boy was left outside overnight on the second occasion, authorities said.

A woman and a man who called 911 seeking help for the boy didn't answer a dispatcher when asked what the teen was doing before he stopped breathing.

Tyler McMillan had a body temperature of 105.6 degrees Fahrenheit when he was taken to the hospital, according to the autopsy report. Tests done after his death also showed a pattern of dehydration, the report states.

The boy had insect bites over his arms and legs and marks on his wrists and ankles that were consistent with plastic ties, according to the autopsy report. He also had bruises on his buttocks and legs that appeared to have been caused by a rod-like instrument, the report states.