Actor Hayden Panettiere is believed to have died after taking an oxycodone tablet laced with fentanyl.

The Heroes actor died in August at age 36 and investigations have been ongoing into the circumstances surrounding her death in South Carolina.

Now, multiple law enforcement sources with direct knowledge of the case have told TMZ that Panettiere had a “long-time drug dealer” in Los Angeles, who provided her with black-market prescription medications. She had taken some of them with her on her flight from California the day before she died.

Authorities are said to be working on the theory Panettiere took the oxycodone pill on the day she died, but it was laced with the strong opioid.

Toxicology results are still pending, but the Drug Enforcement Administration in Los Angeles is piecing together the relationship between the Nashville star and her drug dealer to try to trace the pill back to him.

It was previously revealed that Panettiere’s on-off boyfriend, Brian Hickerson, gave first responders a bag of her prescription medications when they arrived at the apartment they had been staying at when she died.

An autopsy previously found “no signs of trauma” in the Heroes star’s death.

“At autopsy no signs of trauma were discovered that would have contributed to the death,” a statement from Greenville County Coroner’s Office read.

The statement confirmed first responders had found Panettiere suffering a cardiac arrest when they arrived on the afternoon of August 16.

TMZ obtained dispatch audio of the call to emergency services, which appears to pick up officials discussing an overdose.

The short recording included one officer saying: “Responding. Overdose. CPR is in progress.”

After the emergency call, paramedics rushed to the apartment and tried to resuscitate Panettiere using “advanced cardiac life support”.

But after an hour, the Ice Princess star — who had 11-year-old daughter Kaya with former partner Wladimir Klitschko — was pronounced dead.