The Drug Enforcement Administration (DEA) has joined the investigation into the death of actress Hayden Panettiere, according to sources familiar with the matter. The Greenville City Police Department in South Carolina is leading the probe, with the DEA providing assistance.

Panettiere, 36, died on Sunday at a residence in Greenville. The actress was known for her roles in "Heroes," "Nashville," and "Ice Princess." Her death has prompted widespread mourning across Hollywood.

Details from the scene emerged Monday, with a police report indicating that officers responded to an EMS assist for an unresponsive individual. The report stated that Panettiere was with her on-again, off-again boyfriend, Brian Hickerson, and his brother, Zack Hickerson, when she was pronounced dead.

The official cause and manner of Panettiere's death are pending further investigation and the completion of additional studies, according to the coroner's office. It remains unknown if drugs or alcohol were involved at the time of her passing, although Brian Hickerson reportedly showed officers a bag of medication Panettiere was taking.

In May, Panettiere released a memoir, "This Is Me: A Reckoning," in which she candidly discussed her struggles with postpartum depression, addiction, recovery, trauma, domestic abuse, and loss, dating back to her experiences with child stardom and continuing through adulthood.

Panettiere's career spanned several notable projects, including "Remember the Titans," "Raising Helen," and multiple "Scream" films, in addition to her well-known television roles. She is survived by her daughter, Kaya, from her previous relationship with Wladimir Klitschko.

Her ex-boyfriend, Brian Hickerson, was present at the scene when she died, as noted in the police report. The circumstances surrounding the event are still under active investigation by local authorities and now the DEA.

Representatives for Panettiere have been contacted for comment. The involvement of the DEA suggests a potential focus on drug-related aspects of the investigation, though no specific details have been officially confirmed.