The Drug Enforcement Administration is concentrating on a long thread of text messages between Hayden Panettiere and her drug dealer, sources tell TMZ.
The messages reportedly span years and continued until the week she died.
Sources with direct knowledge of the investigation say the texts are now a centerpiece of the probe.
One source described the exchanges as very specific about purchasing black market pills, adding, "There are a slew of messages about drugs."
Fentanyl-Laced Pill Suspected in Death
TMZ previously reported that the DEA believes Panettiere died after taking an oxy pill laced with fentanyl.
According to sources, she brought various pills with her on a flight from Los Angeles to South Carolina the night before she died.
Her boyfriend, Brian Hickerson, gave police a bag of her medications, which could reveal other pills laced with the deadly drug.
Neighbors in West Hollywood told TMZ they had seen three suspicious people -- two women and a man -- coming to Panettiere's unit for years.
They said the visitors would arrive individually, often carrying a small bag, and Panettiere would take the bag before the person left.
The neighbors suspected the three were drug dealers, and the man reportedly showed up with a bag the week she died.
Text messages have helped authorities catch dealers in other cases, notably the Mac Miller case, where the dealer went to prison.
Toxicology results in Panettiere's case will not be available for at least a few weeks.
