Hayden Panettiere reportedly consumed a single oxycodone pill laced with fentanyl the morning she died, according to law enforcement sources who spoke with TMZ. The "Heroes" actress was discovered unresponsive in a South Carolina Airbnb last month.

Investigators told TMZ that Panettiere had a "long time drug dealer" in Los Angeles who allegedly supplied her with black-market prescription drugs. The outlet reported that Panettiere ingested several drugs obtained from this dealer on a flight from Los Angeles to South Carolina the day before her death.

Authorities believe the fatal dose was an oxycodone pill mixed with fentanyl, a synthetic opioid that is significantly more potent than heroin and morphine, according to the Centers for Disease Control and Prevention (CDC). The Drug Enforcement Administration (DEA) is reportedly working to identify the alleged dealer by investigating the relationship between the individual and Panettiere.

Further action is pending the results of Panettiere's toxicology report.