Doctors conducted an autopsy on the body of Michael Jackson on Friday but could not immediately determine what killed the "King of Pop," amid reports he had been injected with a narcotic painkiller shortly before collapsing. Jackson was in full cardiac arrest when paramedics arrived at his rented mansion in the Holmby Hills neighborhood of Los Angeles on Thursday afternoon, with his personal physician trying desperately to revive him. The 50-year-old pop superstar was rushed to nearby UCLA Medical Center, where he was pronounced dead without regaining consciousness. "The cause of death (determination) has been deferred, which means that the medical examiner has ordered additional testing such as toxicology and other studies," Los Angeles County Coroner's spokesman Craig Harvey said. "Those tests we anticipate will take an additional four to six weeks."