Oil heir Andrew Getty had been diagnosed with a brain aneurysm and had not been eating or sleeping well in the days before his death, the mother of his girlfriend said.
Marilynne DeJonge told The Associated Press she has not spoken to her daughter Lanessa DeJonge since Saturday and is worried about her.
She said Lanessa DeJonge met Mr Getty seven years ago and depended on him for housing, and she does not have a phone.
Los Angeles homicide detectives are investigating the death of Andrew Getty, a 47-year-old heir to the Getty oil fortune, at his Hollywood Hills home on Tuesday.
Officers were summoned to the property at 2:18 p.m. local time on Tuesday with a report of an unconscious male, said Officer Norma Eisenman, a spokeswoman for the Los Angeles Police Department.
She said detectives in the robbery-homicide division were investigating. The Los Angeles County Medical Examiner-Coroner was also investigating, according to Lieutenant Larry Dietz.
