Questions remain as details keep emerging in Hayden Panettiere death

As more details continue to emerge in the death investigation of actress Hayden Panettiere, some questions still remain.

The "Heroes" and "Nashville" star, 36, died Aug. 16 at an apartment complex in Greenville, South Carolina, from the "toxic effects of fentanyl" and other drugs, according to a release from the Greenville County Coroner's Office. An investigative report later revealed fentanyl-laced pills and an unidentified white powder were found with the former child star when she died.

Now, as investigators reveal more details about the circumstances surrounding Panettiere's death, here's what we know and are looking out for as the investigation continues.

Panettiere died from the "toxic effects of fentanyl, 4-ANPP, Alprazolam, Methocarbamol and Quetiapine," according to a Greenville County Coroner's Office release. Fentanyl is a synthetic opioid drug that is used to relieve pain and is around 100 times more potent than morphine and 50 times more potent than heroin as an anesthetic, according to the Drug Enforcement Administration.

The "manner of death has been ruled accident," and no signs of trauma were discovered that would have contributed to Panettiere's death, the release added.

At the scene of her fatal overdose, authorities found a bottle of Adderall as well as blue pressed pills and a cut straw that tested positive for fentanyl inside Panettiere's makeup bag, according to the USA TODAY Network's Greenville News, which obtained the investigative report from the Greenville County Medical Examiner.

Other prescription bottles were also found on the kitchen table, and glass vials and prefilled and empty syringes were found in a small lunchbox inside the refrigerator, the report said.

The investigative report also shared that unidentified white powder in a small, clear plastic bag was found inside a sunglasses case packed in the actress' suitcase. It was not immediately clear whether the white powder found in her suitcase was tested or identified, the report added.

Panettiere's on-and-off boyfriend Brian Hickerson and his brother, Zach Hickerson, were on the scene and called 911 when the actress went into cardiac arrest. Now, investigators are revealing what Hickerson told them after her fatal overdose.

Brian Hickerson told investigators that the couple had arrived in South Carolina the night before, according to the Greenville County investigative report obtained by Greenville News.

In the morning, Panettiere woke up and put on makeup, he said, and the pair ate cereal together before he fell back asleep. Brian Hickerson said he woke up in the afternoon to Zach Hickerson knocking on his door so the trio could go to lunch, but upon going to wake up Panettiere, they found her "crisscross applesauce," face down and unresponsive on a sofa bed.

Brian Hickerson said he administered multiple cans of Narcan, a nasal spray that can reverse life-threatening opioid overdoses, but nothing changed. He told his brother to call 911, and they started CPR until emergency personnel arrived.

One of the brothers told the deputy that Panettiere had a long history of drug, alcohol and nitrous oxide abuse.

The report also said that a redacted name, assumed to be Brian Hickerson, was not aware of Panettiere using any illegal substances that day or the day prior, but said that she was very good at hiding them and that he had administered Narcan to her before.

On Sept. 12, nearly a month after the "Remember the Titans" actress' death, her boyfriend, Brian Hickerson, was briefly detained by police following a reported assault at Wild Wing Café in Greenville, South Carolina. The 38-year-old was among the "multiple patrons" detained in the alleged altercation but was later released at the scene with no charges.

Police also arrested his brother Zach Hickerson – who was reportedly "highly intoxicated" and "began yelling profanities in a public setting" – and later booked him into the Greenville County Detention Center. He was released the following day after paying a $150 fine on Sept. 23, court records reviewed by USA TODAY Sept. 24 showed.

Zach Hickerson's case has since been disposed of.

Questions still remain about the source of the fentanyl-laced pills.

Investigators with the DEA and other departments, from both Los Angeles and South Carolina, are focused on identifying what drugs contributed to her death and where those drugs came from, according to ABC News, citing unnamed sources.

The department has not commented on the state of the investigation, simply noting it is "active" and telling Greenville, South Carolina, station WYFF4 that "these cases are complex and take time to develop."