A coroner says the cause of death for a 4-year-old Pennsylvania boy found dead in a septic tank was drowning.

But Beaver County Coroner Teri Tatalovich-Rossi said Tuesday that she couldn't determine the circumstances of Wyatt Smitsky's death. State police are investigating whether his drowing was intentional or an accident.

Wyatt's body was found Sept. 5 after searchers drained a septic tank on property near his home in Greene Township, about 25 miles northwest of Pittsburgh.

The boy was playing with two young sisters when he went missing, prompting an 18-hour search.

A district attorney has said it's possible that Wyatt moved the tank's 14-pound lid by himself.