A 1-year-old Pennsylvania girl's sudden death in August resulted from accidental exposure to the elephant tranquilizer carfentanyl (or carfentanil), a synthetic drug 10,000 times more potent than morphine.

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

County police are still investigating the death of the girl who was found unresponsive Aug. 6 at a home in McKees Rocks. The girl's mother has posted on Facebook that a baby sitter was watching the girl when she overdosed.

Police 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 the Drug Enforcement Administration says is 100 times stronger than fentanyl, another synthetic opioid that is 50 times more potent than heroin.

The girl would have turned 2 this week.