California Attorney General Jerry Brown's office said records of the prescription in the name of the former teen heartthrob were found during an investigation of the ring that illegally obtained prescription pads and used the stolen identities of doctors to fill them out.
"Corey Haim's death is yet another tragedy linked to the growing problem of prescription drug abuse," Brown said in a written statement. "This problem is increasingly linked to criminal organizations, like the illegal and massive prescription drug ring under investigation."
Los Angeles County coroner's officials, however, said they have not yet determined what killed the 38-year-old Haim on Wednesday.
State law enforcement authorities said they were investigating the drug ring and how the name of Haim, who battled addiction for years, appeared on the prescription.
Javier Salaiz, an investigator with the state attorney general's office, said authorities have not yet confirmed that Haim actually filled the prescription or if someone was using his name to acquire the prescription.
However, a person familiar with the investigation who spoke on condition of anonymity because the case is ongoing said Haim may have been doctor shopping.
Assistant Chief Coroner Ed Winter said four prescription drug bottles bearing the actor's name were found in the apartment where he collapsed, but all those drugs had been provided by a doctor who had been treating the actor.
The coroner's office has declined to state what medications were discovered, but said no illegal drugs were found.
Winter said no determination had been made about Haim's cause of death, and toxicology tests would not be available for at least a month.
He said he had not been contacted by the attorney general's office.
"It surprises me that Jerry Brown would come out and give a cause of death," he said.
Brown said later in an interview that he didn't know what killed Haim.
The illegal prescription was for the powerful painkiller OxyContin, he said.
"This is a growing and dangerous problem," Brown said.
Christine Gasparac, a spokeswoman for Brown, said the prescription was found through the state's computer database that tracks prescriptions that are filled.