Los Angeles County coroner's spokesman Craig Harvey says determining the cause of Michael Jackson's death will require further neuropathology and pulmonary tests that will take four to six weeks.
Harvey says there were no signs of foul play or trauma to the body during the three-hour autopsy. He also says Jackson was taking some unspecified prescription medications.
The spokesman says Assistant Chief Coroner Ed Winter is with Jackson's family.
Harvey says the police department has requested a security hold on the investigation which limits how much the coroner's office can say about the case. He says the death became a coroner's case because there was no doctor to sign the death certificate.
Harvey says the body will be released once the family selects a mortuary.
A person with knowledge of the situation told The Associated Press that Jackson, who was with a cardiologist when he collapsed at his rented home in Los Angeles, appeared to have suffered a heart attack.
The person, who was not authorized to speak publicly and requested anonymity, said Jackson suffered a heart attack, which is a blocking of the arteries that can cause cardiac arrest. Jackson's brother Jermaine said Thursday that it was believed the pop singer went into cardiac arrest, often but not always due to a heart attack.
A heart attack would not rule out drugs playing a role in his death, but could also indicate a long-term problem such as heart disease.
The lack of scientific evidence hasn't stopped the concerns of friends and speculation by tabloids that drugs were involved, reports CBS News correspondent Bill Whitaker. The London tabloid, The Sun, and celebrity Website TMZ claim Jackson was injected with the painkiller Demerol shortly before he died, and there have been reports that Jackson was addicted to the painkiller Oxycontin. Those who knew him best fear the worst.
"Michael has been using medications for quite a while," said former Jackson attorney Brian Oxman. "I have warned of this happening, the enablers around him have done this and i am so saddened."
In a call this morning to the Early Show's Harry Smith, Jackson friend Liza Minelli voiced the same fear.
"I'm sure when the autopsy comes, all hell's gonna break loose, so thank God we're celebrating him now," she said.
Police now are seeking the doctor who was in the house when the pop icon collapsed, Dr. Conrad Robert Murray, reports Whitaker. Yesterday, police impounded the car he was driving at Jackson's mansion.
Today, in a gut-wrenching blog, Jackson's former wife, Lisa Marie Presley, daughter of that other king, Elvis Presley, writes that Jackson feared he'd die like Elvis, who overdosed on drugs: "I'm afraid I'm going to end up like him, the way he did." Then she goes on, "Our relationship was not a sham. I do believe he loved me as much as he could love anyone and I loved him very much."
Police earlier today seized the car of Dr. Conrad Murray, a cardiologist who practices in California, Nevada and Texas, who was with Jackson at the time of his death. Police said they believed the car may contain drugs or other evidence.
Heart attacks often lead to cardiac arrest, where the heart rhythm is disrupted and the heart stops pumping blood, said Dr. Douglas Zipes, an Indiana University heart specialist and past president of the American College of Cardiology.
When autopsies are done on cardiac arrest victims, as many as three-fourths show signs of heart disease, such as clogged arteries, he said.
Finding signs of a heart attack would not rule out drugs playing a role. For example, injections of the powerful painkiller Demerol can depress normal breathing or cause a sudden drop in blood pressure and trigger a heart rhythm problem, said Dr. Lance Becker, a University of Pennsylvania emergency medicine specialist and an American Heart Association spokesman.
If that occurred in someone who already had clogged arteries, it could make the situation much worse, he said.
In a, a caller reports Jackson was on a bed and not breathing or responding to CPR. The unidentified caller said Jackson was with his personal doctor at the time.
"I need an ambulance as soon as possible, sir," the caller said urgently but politely. "We have a gentleman here that needs help and he's not breathing yet. He's not breathing and we need to - we're trying to pump him, but he's not, he's not."
The pop star died later Thursday afternoon at UCLA Medical Center.
More Michael Jackson coverage:
Quincy Jones: "I Miss My Little Brother"
Motown's Gordy On Discovering Jackson
Gary, Indiana Mourns Hometown Star
The Man With The Moves
King Of Pop Lived In Luxury, Died In Debt
Coroner: Cause Of Jackson Death Deffered
911 Caller: Jackson "Not Breathing"
KHOU: Texas MD With Jackson Amid Collapse
A Collection Of CBS Videos Of Michael Jackson
The Death Of Michael Jackson, Full Coverage