OMAHA, Neb. (AP) — Preliminary autopsy results show a 54-year-old Omaha woman died of blunt force trauma to her head and her son died of what appears to have been carbon monoxide poisoning.

A news release from the Douglas County Sheriff’s Office on Friday said investigators are still awaiting toxicology results to confirm the cause of Cooper Flanagan’s death.

His body and that of his mother, Maureen Flanagan, were found Wednesday morning in their northwest Omaha home. Hers was discovered in the basement. His was found in a car in the garage.

Chief Douglas County Deputy Sheriff Thomas Wheeler told The Associated Press that investigators have considered the possibility that the 18-year-old attacked his mother before taking his own life, “but we want to rule out any other possibility before we make a statement.”