Hayden Panettiere's death ruled accidental by police

Actress Hayden Panettiere's death has been ruled accidental, according to police in South Carolina, who said Wednesday they are closing their investigation.

"Based on the Medical Examiner’s determination and the findings of the investigation, Hayden Panettiere’s death has been ruled accidental," the Greenville Police Department said in a statement, adding that the department has "concluded its investigation."

Panettiere, 36, died in August after she was found unresponsive at an apartment in Greenville, South Carolina.

ABC News has reached out to a representative for Panettiere's family for comment.

The police department's announcement comes more than a month after the Greenville County Coroner's Office in South Carolina ruled her death an accidental overdose involving fentanyl and other substances. Police had continued their investigation after the coroner released its findings.

In its Sept. 22 findings, the coroner's office identified the cause of death as the toxic effects of fentanyl, 4-ANPP, alprazolam, methocarbamol, and quetiapine. The autopsy found no signs of trauma that contributed to her death.

4-ANPP is a byproduct of fentanyl production; alprazolam, known as Xanax, treats anxiety and panic disorders; methocarbamol, known as Robaxin, is a muscle relaxant; and quetiapine, known as Seroquel, is an antipsychotic medication.

Of the combination of medications, fentanyl is the most likely to result in an overdose death.

Panettiere's on-again, off-again boyfriend, Brian Hickerson, and his brother, Zach Hickerson, were at the apartment when officers responded, according to a police report obtained by ABC News.

Emergency responders attempted life-saving measures before Panettiere was pronounced dead, according to the report.

The U.S. Drug Enforcement Administration had also been assisting police with the investigation, sources familiar with the matter previously told ABC News.

The DEA’s investigation is believed to be ongoing and could be looking into street-level drug dealers who may have provided drugs to the late actress, sources said.

Prior to her death, Panettiere had spoken publicly about her experiences with addiction and recovery, as well as the challenges she faced growing up in the entertainment industry.

The actress, who was known for her roles in "Ice Princess," "Heroes" and "Nashville," released a memoir in May titled, "This Is Me: A Reckoning." In the book, she discussed postpartum depression, addiction and recovery, trauma, domestic abuse and loss, according to its synopsis.

Panettiere is survived by her daughter Kaya, whom she shared with her ex-fiance Wladimir Klitschko.

A memorial service for Panettiere was held in Malibu in September. It was attended by around 80 friends of the late actress, her representative told ABC News at the time.