As grief for the King of Pop poured out around the world, from the icons of music to heartbroken fans, an autopsy showed no sign of trauma to Jackson, whose death came just weeks before he was to launch an epic comeback bid in a series of 50 concerts in London.
The person, who was not authorized to speak publicly and requested anonymity, said Jackson had suffered a heart attack. Jackson's brother Jermaine had said the pop singer apparently went into cardiac arrest — which often but not always happens because of a heart attack.
Authorities said they would speak with the doctor, identified by the Los Angeles Times as cardiologist Conrad Murray, and said they had towed his car from Jackson's rented mansion because it could contain medication or other evidence. Police stressed that the doctor was not a criminal suspect.
Deputy Police Chief Charlie Beck said he hoped the doctor would shed light on the coroner's findings and "lead us to some conclusions."
Craig Harvey, a spokesman for the Los Angeles County coroner, said there were no signs of foul play. He said Jackson was taking some unspecified prescription medication but gave few other details.
A 911 call released by fire officials shed light on the desperate effort at the mansion to save Jackson's life before paramedics arrived Thursday afternoon. Jackson died later at UCLA Medical Center.
In the recording, an unidentified caller pleads with authorities to send help, offering no clues about why Jackson was stricken. He tells a dispatcher that Jackson's doctor is performing CPR.
"He's pumping his chest," the caller says, "but he's not responding to anything."
Asked by the dispatcher whether anyone saw what happened, the caller answers: "No, just the doctor, sir. The doctor has been the only one there."
The autopsy was completed in a matter of hours, but an official cause of death could take up to six weeks while medical examiners await toxicology tests. No funeral plans had been made public.
Jackson had remained out of the public spotlight during intense rehearsals for the London concerts. Lou Ferrigno, the star of "The Incredible Hulk," said he had been working out with Jackson for the past several months.
Still, Jackson's health had been known to be precarious in recent years, and one family friend said Friday that he had warned the entertainer's family about his use of painkillers.
"I said one day we're going to have this experience. And when Anna Nicole Smith passed away, I said we cannot have this kind of thing with Michael Jackson," Brian Oxman, a former Jackson attorney and family friend, told NBC's "Today" show. "The result was I warned everyone, and lo and behold, here we are. I don't know what caused his death. But I feared this day, and here we are."
Oxman claimed Jackson had prescription drugs at his disposal to help with pain suffered when he broke his leg after he fell off a stage and for broken vertebrae in his back.
The worldwide wave of mourning for Jackson continuted unabated for the man who revolutionized pop music and moonwalked his way into entertainment legend.
"My heart, my mind are broken," said Elizabeth Taylor, who was one of Jackson's closest frineds and married one of her husbands at a lavish wedding at the pop star's Neverland Ranch in 1991. She said she had heard the news as she was preparing to travel to London for Jackson's comeback show, and added, "I can't imagine life without him."
Hundreds made a pilgrimage to the Jackson family's compound in Los Angeles, leaving flowers and messages of love. They did the same at his star on the Hollywood Walk of Fame and at the home in Los Angeles' Holmby Hills where Jackson was stricken. Some camped out overnight.
In New York, people stopped at Harlem's Apollo Theater, where Jackson had performed as a child with his brothers in one of rock's first bubblegum supergroups, the Jackson 5.