Stacy Dawn Murphy, the most recent of three deaths at Narconon Arrowhead, died of an accidental overdose of oxymorphone, a prescription drug, according to a preliminary report released Tuesday by the state Medical Examiner's Office.
Murphy's death at Narconon, a drug rehabilitation facility northeast of McAlester on Lake Eufaula, spurred an ongoing, multi-agency investigation into the facility's practices.
The full autopsy report is still being completed, according to a spokeswoman for the Medical Examiner's Office.
Murphy, 20, of Owasso died July 19 at Narconon after returning to the facility from a short leave of absence.
Narconon Arrowhead is the flagship branch of an international drug-rehabilitation organization rooted in the teachings of Scientology founder L. Ron Hubbard.
Murphy's family has a lawsuit pending against the Narconon program alleging a wrongful death and negligence.
Gary Richardson, the attorney for Murphy's family, said the medical examiner's preliminary report proves what the family has known since her death.
"As far as the determination of acute oxymorphone, that more or less comports with what we have understood from what we learned at the beginning," Richardson said. "Which simply says this young girl was not taken care of."
When Murphy returned to Narconon, she was determined to be intoxicated, according to the family's lawsuit.
She was allegedly taken to the onsite Withdrawal Unit the night of July 18 and was not correctly monitored before she was found dead at about 9:20 a.m., the lawsuit alleges.
Oxymorphone is an opiate used to relieve moderate to severe pain, according to the U.S. National Library of Medicine website. The drug works by changing how the body responds to pain.
The investigation in the case has been led by the Oklahoma State Bureau of Investigation, Pittsburg County Sheriff's Office and the Oklahoma Department of Mental Health.
Officials with the Department of Mental Health have said the official autopsy report is one of several things they have been waiting on to complete their investigation, said Jeff Dismukes, spokesman for the Oklahoma Department of Mental Health and Substance Abuse Services.
Other recent deaths at the facility include those of Gabriel Graves, 32, of Claremore and Hillary Holten, 21, of Carrollton, Texas.
Graves died Oct. 26, 2011, and Holten died April 11.
Graves' and Holten's full autopsy reports have been released, but their cause and manner of death were undetermined, according to the state medical examiner reports.
The families of Graves and Holten have also filed civil lawsuits against Narconon alleging negligence.