BUFFALO, Mo. (AP) - The cause of death for a southwest Missouri teenager whose body was found weighted down in a lake is still a mystery. Benton County Coroner Jim Miller said Monday that the autopsy on 15-year-old Khighla Parks of Willard did not determine a cause of her death. Her body was found Sept. 30 in Truman Lake. Miller says the autopsy found no sign of trauma, disease or drug use. She had only an insignificant amount of alcohol in her blood. The Springfield News-Leader reports Miller said asphyxiation remains a possible cause of death. Park's death has been ruled a homicide. A Springfield man, 47-year-old Anthony Balbirnie, is charged with abandonment of a corpse. Park was last seen with Balbirnie at a home in Buffalo Sept. 21.