Carrie Fisher died from sleep apnea and a combination of other factors, but investigators were not able to pinpoint an exact cause, coroner’s officials said Friday.

Among the factors that contributed to Fisher’s death was buildup of fatty tissue in the walls of her arteries, the Los Angeles County coroner’s office said in a news release late Friday. The release states that the “Star Wars” actress showed signs of having taken multiple drugs, but investigators could not determine whether they contributed to her death in December.

Her manner of death would be listed as undetermined, the agency said.

Sleep apnea is a condition in which a person’s breathing pauses during sleep. The pauses may be brief or last several minutes, according to information from the National Institutes of Health.

Fisher, 60, suffered a medical emergency on an international flight on Dec. 23 and died four days later. Her mother, longtime movie star Debbie Reynolds, died the following day.

The actresses were laid to rest together at Forest Lawn-Hollywood Hills, a cemetery where numerous celebrities are buried.

Fisher’s brother, Todd Fisher, said he was not surprised by the results. He added that his family did not want a coroner’s investigation of his sister’s death. “We’re not enlightened. There’s nothing about this that is enlightening,” he said.

“I would tell you, from my perspective that there’s certainly no news that Carrie did drugs,” Todd Fisher said. He noted that his sister wrote extensively about her drug use, and that many of the drugs she took were prescribed by doctors to try to treat her mental health conditions.

Fisher long battled drug addiction and mental illness. She said she smoked pot at 13, used LSD by 21 and was diagnosed as bipolar at 24. She was treated with electroshock therapy and medication.

“I am not shocked that part of her health was affected by drugs,” Todd Fisher said.

He said his sister’s heart condition was probably worsened by her smoking habit, as well as the medications she took. “If you want to know what killed her, it’s all of it,” he said.