A toxicology report shows that the 13-year-old Port Angeles girl found dead while camping in August died of a methadone overdose.
Clallam County sheriff's Sgt. Lyman Moores says the report indicated Lillian Star Taylor took about 10 pills - a surprising amount for a girl her age.
The Peninsula Daily News reported Wednesday that detectives are investigating how she got the pills.
Lillian was camping with her mother and a few of her mother's friends near Beaver on the Olympic Peninsula when the girl was found dead in a tent.
Methadone is a narcotic commonly used by people trying to stop using heroin.