New details on investigation into Hayden Panettiere's death

The investigation into the death of actress Hayden Panettiere is now a cross-country investigation in both Los Angeles and South Carolina, sources told ABC News.

While toxicology reports are still pending, sources say investigators are focusing on what drugs may have played a role in her death, and where the drugs came from.

Panettiere, known for her roles in "Heroes," "Nashville" and "Ice Princess," died on Aug. 16 after she was found unresponsive and in cardiac arrest at a residence in Greenville, South Carolina.

First responders attempted to resuscitate her, but she was pronounced dead at the scene.

Panettiere's official cause and manner of death have not yet been announced.

The actress flew from Los Angeles to South Carolina the day before her death, sources say.

The Greenville City Police Department is leading the investigation into Hayden Panettiere's death, with the U.S. Drug Enforcement Administration assisting, sources familiar with the matter told ABC News last month.

In response to DEA joining the investigation into her death, a representative for Panettiere told ABC News in an Aug. 20 statement, "There's nothing to be shared at this time as the investigation is ongoing but we are hopeful that justice will be served."

Sources told ABC News the investigation into Panettiere's death could be looking into street-level drug dealers who may have provided drugs to the late actress.

Brian Hickerson, Panettiere's on-again, off-again boyfriend, and his brother Zach Hickerson were present at the scene of her death, according to a police report previously obtained by ABC News. The responding police officer added in the report that Brian Hickerson showed them “the bag of medication Hayden is currently on.”

The report noted that Panettiere had been "temporarily staying" at the residence where she was found.

Brian Hickerson's attorney shared a statement with ABC News on Aug. 20, in response to the police report, writing, "Hayden's death remains under investigation and it is important to allow that investigation to proceed. As has been publicly reported, police confirmed there were no signs of foul play."

"Out of respect for Hayden's loved ones and the ongoing investigation, there will be no further comment at this time," the statement added.

Prior to her death, Panettiere opened up about her substance abuse issues, which she said ran concurrent with her successful acting career. The actress wrote about her struggles in her memoir "This Is Me: A Reckoning," released in May, and spoke about them in press interviews.