Nearly a month after Hayden Panettiere’s sudden death at 36, investigators are still trying to answer one of the biggest questions surrounding her final hours.

What, exactly, caused her death?

Now the investigation has taken another significant turn.

Brian Hickerson, Panettiere’s on-again, off-again boyfriend who was present at the South Carolina residence where she was found unresponsive, has met with officials from the Drug Enforcement Administration, according to a source close to the investigation.

And he apparently is not the only person authorities have spoken with.

The source told PEOPLE that investigators have “interviewed others” as they continue examining the circumstances surrounding the Heroes and Nashville star’s death. Toxicology results, which could provide critical answers about what substances were in Panettiere’s system, have still not been returned.

Meanwhile, authorities are reportedly exploring whether a drug dealer may have supplied Panettiere with substances before she died.

That does not mean investigators have concluded drugs caused her death, nor has Hickerson been accused or charged with any crime connected to Panettiere’s death.

For now, the investigation remains open.

The DEA Meeting Marks a New Development

Panettiere died on Aug. 16 at a residence in Greenville, South Carolina, just days before what would have been her 37th birthday.

Police responded after a 911 call reported an unresponsive woman. Emergency medical personnel attempted lifesaving measures, but Panettiere was pronounced dead.

According to the Greenville County Coroner’s Office, she had been found in cardiac arrest.

An autopsy was completed the following day.

Coroner Mike Ellis said investigators found no signs of trauma that contributed to her death, while stressing that the investigation remained active.

That left toxicology testing particularly important.

Such testing can take weeks and may help determine whether prescription medications, illicit substances, alcohol or some combination of factors contributed to a death.

Until those results are complete, authorities have not announced an official cause and manner of death.

But the involvement of the DEA has added another dimension to the case.

The Greenville City Police Department remains the lead agency, while the DEA is assisting with the investigation, ABC News previously reported.

PEOPLE now reports that Hickerson personally met with DEA officials.

Investigators Reportedly Looking at a Possible Dealer

Citing reporting originally published by TMZ, PEOPLE said investigators are pursuing the possibility that someone may have sold Panettiere drugs before her death.

One source described authorities as “zeroing in on a potential drug dealer.”

That remains an investigative lead, not a final finding.

There has been no official determination that illegally obtained drugs caused Panettiere’s death, and the pending toxicology report could significantly change or clarify the direction of the case.

The distinction is important.

Federal drug investigators becoming involved does not automatically mean a crime occurred or that anyone who was present when Panettiere died is considered a suspect.

Hickerson, specifically, has not been accused or charged with wrongdoing in connection with her death.

His attorney, Sloan Ellis, declined to comment on the latest report that he had met with the DEA.

Previously, Ellis emphasized that police had reported finding no evidence of foul play and asked that investigators be allowed to complete their work before conclusions were drawn.

Hickerson and His Brother Were There When First Responders Arrived

Hickerson’s presence in Greenville has been part of the public record since shortly after Panettiere’s death.

A police report obtained by ABC News and PEOPLE states that both Brian and his brother, Zach Hickerson, were at the residence while emergency personnel attempted to revive the actress.

The responding officer wrote that there did not appear to be an obvious physical explanation for why Panettiere was unresponsive.

EMS continued lifesaving efforts for an extended period before she was pronounced dead.

During the response, Brian showed police a bag containing medications Panettiere had been taking.

Zach reportedly described Panettiere to authorities as his brother’s girlfriend, confirming that the complicated relationship between Panettiere and Hickerson had continued.

The officer also documented the brothers’ reactions during the emergency, noting that Zach appeared extremely emotional while paramedics were working on Panettiere and that Brian did not visibly become emotional until she was declared dead.

That observation has attracted considerable attention, but it is simply part of the responding officer’s report. Authorities have not cited it publicly as evidence that Hickerson committed any crime.

Their Relationship Had a Troubled History

Panettiere and Hickerson were first linked in 2018 following her split from former fiancé Wladimir Klitschko, with whom she shared daughter Kaya.

Their relationship later became associated with serious legal problems.

Hickerson was arrested on domestic violence-related charges during the relationship.

In 2020, Panettiere released a public statement saying she hoped speaking about what she had experienced would help other people in abusive relationships seek support.

In April 2021, Hickerson pleaded no contest to two felony counts of injuring a spouse or girlfriend stemming from his 2020 arrest. He received probation, domestic violence classes and jail time. Other charges were dropped, while a separate 2019 case was dismissed.

Years later, however, the two were again in each other’s lives.

Just three days before Panettiere’s death, Hickerson had faced another unrelated legal setback.

A California court rejected his effort to reduce his prior felony domestic violence convictions to misdemeanors and expunge the case. Prosecutors opposing his petition had also cited allegations of continued drug use, according to court records obtained by PEOPLE.

Those allegations are separate from the investigation into Panettiere’s death.

Panettiere Had Been Open About Addiction

Panettiere had spoken publicly about her own history with alcohol and opioids.

In a 2022 interview with PEOPLE, she described an earlier period of her life as deeply troubled and acknowledged struggling privately with addiction.

Her openness made the circumstances surrounding her sudden death especially painful for fans who had watched her work to rebuild her health and career.

But her past addiction does not establish what happened on Aug. 16.

That is precisely what investigators are still trying to determine.

The toxicology report could prove to be one of the most important pieces of evidence.

Until it is complete, reports about possible drugs or a potential supplier remain part of an ongoing investigation rather than a confirmed cause of death.

The Biggest Questions Remain Unanswered

Panettiere’s death shocked fans who had watched her grow up onscreen.

She appeared as a child actor in projects including Remember the Titans before becoming internationally known as cheerleader Claire Bennet on NBC’s Heroes. She later earned acclaim as country singer Juliette Barnes on Nashville.

She was only 36 when she died.

Her family remembered her as a person who brought enormous love and joy to those around her and to the millions who knew her through her work.

Now, almost a month later, the investigation has moved well beyond the initial response at the Greenville residence.

An autopsy has been performed.

Police say no contributing trauma was found.

The DEA has joined the investigation.

Hickerson has met with federal officials.

Other people have reportedly been interviewed.

And investigators are looking into the possibility that someone supplied Panettiere with drugs before her death.

Yet the most consequential piece of information remains missing.

The toxicology results have not come back.

Until they do — and until investigators determine what, if anything, those results reveal about Panettiere’s final hours — the case remains exactly what authorities say it is:

ongoing.