The investigation into Hayden Panettiere’s death has stretched from coast to coast, with federal authorities now looking into whether the actress obtained illicit — and possibly counterfeit — drugs from a dealer in Southern California, a source familiar with the investigation tells CNN. Medics responding to a 911 call on Aug. 16 found Panettiere in cardiac arrest at an apartment in Greenville, South Carolina, and were unable to resuscitate her. The Greenville County coroner has not released an autopsy report or the 36-year-old’s cause or manner of death, citing pending toxicology tests. Drug Enforcement Administration agents and Los Angeles-area authorities have questioned several people about the circumstances surrounding the California resident’s death, the source familiar with the case said, and are examining the possibility she may have died after taking a counterfeit pill that she believed was another substance. The source said the pending toxicology testing will be critical in helping investigators determine whether she ingested a counterfeit narcotic, and how it may have interacted with any other substances in her body at the time of her death. While investigators have conducted investigative activity in the Los Angeles area, where Panettiere lived, and in Greenville, where she died, the source said authorities would be examining any other geographic areas the investigation may lead them to. CNN has sought comment from the DEA, the FBI and authorities in Los Angeles and Greenville. As CNN has previously reported, law enforcement across the country has been aggressively pursuing dealers who illicitly sell realistic-looking pills resembling prescription medication that are actually made from cheaper and deadlier substances, with some dealers prosecuted for murder after their products killed customers. Panettiere’s representative, Kasey Kitchen, said in a statement to CNN that “Hayden’s death remains under investigation pending the completion of toxicology results, despite reports from some outlets stating otherwise.” “Recent reports attributed to unnamed sources are unverified hearsay and have attributed to conflicting information that continues to circulate,” she added. “While we are all eager to find closure and better understand the circumstances surrounding her passing, we must remain patient and allow the investigative process to unfold.” The actress, whose career started before she was 1 year old, has spoken publicly about her battles with depression and substance abuse. Panettiere’s boyfriend, Brian Hickerson, and his brother Zach called 911 to report Panettiere was unresponsive the afternoon of Aug. 16, a Greenville police incident report said. Brian Hickerson showed an officer a bag of Panettiere’s medications, the report said. Many details in the police report are redacted; no list of medication appeared in the unredacted portion. Panettiere “had been temporarily staying” at the apartment, the coroner’s office said. Authorities did not say whose apartment it was. According to the police report, Brian Hickerson lives in California, and Zach Hickerson lives in Georgia. The Hickersons have roots in Greenville, where some family members live. Investigators found “no signs of foul play during the initial response and investigation,” Greenville police said on Aug. 20. An autopsy performed Aug. 17 revealed no signs of trauma that would have contributed to Panettiere’s death, the coroner’s office said. CNN has sought comment from Brian and Zach Hickerson. “Hayden’s death remains under investigation and it is important to allow that investigation to proceed,” Ellis Hinton, the law firm representing Brian Hickerson, said in an August statement to CNN. “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.” By Josh Campbell, Holly Yan, CNN CNN’s Jason Morris, Dianne Gallagher and Elizabeth Wagmeister contributed to this report.