LUNENBURG, Mass. (AP) – The district attorney says an autopsy has shown accidental carbon monoxide poisoning as the cause of death of a boy found unconscious in a car last week.

Nine-year-old Alejandro Thomasian of Fitchburg was four-wheeling Friday night in the woods near Lunenburg with another boy and three adults when one of the vehicles got stuck.

Thomasian died Sunday, while the other boy, 11-year-old Jobanny Matias of Leominster, has been upgraded to stable condition at Massachusetts General Hospital.

Worcester District Attorney Joseph Early Jr. says an investigation by his office and local police is continuing.

AP-ES-04-28-08 1746EDT