Jackson's body was shifted to a mortuary on Friday night after a three-hour autopsy.
Investigators said the revelation of the exact cause of death has been delayed pending toxicological tests, which take four to six weeks.
According to Brian Elias of the Los Angeles County coroner's office, Jackson's family has told the office that they wanted a second autopsy carried out.
Jackson, 50, apparently got an injection of Demerol, a strong painkiller similar to morphine, shortly before he was rushed to the hospital in deep coma by fire department paramedics Thursday afternoon. He was pronounced dead later at the hospital.
Jackson had been reportedly addicted to Demerol for about 20 years.
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