(AP) - The final act of Michael Jackson's life cameinto clearer focus Friday, a picture of a fallen superstar workingout with TV's "Incredible Hulk" and under the care of his ownprivate cardiologist as he tried to get his 50-year-old body inshape for a grueling bid to reclaim his glory.

While the exact circumstances of his death remained unclear,early clues suggested he may simply have pushed his heart too far. Police said they had towed the doctor's BMW from Jackson's homebecause it may include medication or other evidence, and a sourcefamiliar with the situation told The Associated Press that a heartattack appeared to have caused the cardiac arrest that led to thepop icon's sudden death.

As grief for the King of Pop poured out from the icons of musicto heartbroken fans, and the world came to grips with losing one ofthe most luminous celebrities of all time, an autopsy showed nosign of trauma or foul play to Jackson, who died Thursday at UCLAMedical Center after paramedics not could not revive him.

The AP source who said Jackson apparently suffered a heartattack was not authorized to speak publicly and requestedanonymity. Jackson's brother Jermaine had said the pop singerapparently went into cardiac arrest - which often, but not always,happens because of a heart attack.

Authorities said they spoke with the doctor briefly Thursday andFriday and expected to meet with him again soon. Police stressedthat the doctor, identified by the Los Angeles Times ascardiologist Conrad Murray, was not a criminal suspect.

"We do not consider him to be uncooperative at this time,"Beck said. "We think that he will assist us in coming to the truthof the facts in this case."

Craig Harvey, a spokesman for the Los Angeles County coroner,said there were no signs of foul play in the autopsy and furthertests would be needed to determine cause of death. He said Jacksonwas taking some unspecified prescription medication but gave fewother details.

Meanwhile, a 911 call released by fire officials shed light onthe desperate effort at the mansion to save Jackson's life beforeparamedics arrived Thursday afternoon. Jackson died later at UCLAMedical Center.

In the recording, an unidentified caller pleads with authoritiesto send help, offering no clues about why Jackson was stricken. Hetells a dispatcher that Jackson's doctor is performing CPR.

"He's pumping his chest," the caller says, "but he's notresponding to anything."

Asked by the dispatcher whether anyone saw what happened, thecaller answers: "No, just the doctor, sir. The doctor has been theonly one there."

The president of the company promoting Jackson's shows saidMurray was Jackson's personal physician for three years. Jacksoninsisted Murray accompany him to London, said Randy Phillips,president of AEG Live.

Phillips quoted Jackson as saying: "Look, this whole businessrevolves around me. I'm a machine, and we have to keep the machinewell-oiled." Phillips said Jackson submitted to at least fivehours of physicals that insurers had insisted on.

On Friday, the autopsy was completed in a matter of hours, butan official cause of death could take up to six weeks while medicalexaminers await toxicology tests. No funeral plans had been madepublic.