MCKEES ROCKS, Pa. (AP) — A 1-year-old Pittsburgh-area girl's sudden death in August resulted from accidental exposure to carfentanil, an elephant tranquilizer sometimes mixed with heroin.

The Allegheny County medical examiner says the drug was found in the system of Au'Driana Cohen.

The girl was found unresponsive Aug. 6 at a home in McKees Rocks. Her mother has posted on Facebook that a baby sitter was watching the girl when she overdosed.

County police are still investigating the death. They have yet to identify or charge anybody in connection with the girl's death.

The medical examiner has ruled the girl was accidentally exposed to the drug, which is far more potent than heroin. Even tiny amounts of carfentanil can be lethal.

The girl would have turned 2 this week.