Carrie Fisher died from sleep apnea and a combination of other factors, but investigators have been unable to pinpoint an exact cause, say coroner's officials.

Among the factors that contributed to Fisher's death was the build-up of fatty tissue in the walls of her arteries, the Los Angeles county coroner's office said on Friday.

The Star Wars actress showed signs of having taken multiple drugs, but investigators could not determine whether they contributed to her death in December.

The manner of her death would be listed as undetermined, officials said.

They have not responded to a request for additional details about whether a full autopsy report and toxicology results are available.

Sleep apnea is a condition where 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. Her mother, veteran movie star Debbie Reynolds, died the following day.

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

Fisher's brother, Todd, said he was not surprised by the results.

He added that his family did not want a coroner's investigation into his sister's death. "We're not enlightened. There's nothing about this that is enlightening," he said.