It was speculated before that Xanax side effects caused Michael Jackson's death. Some others blamed it to lupus disease. And according to LaToya Jackson, Michael Jackson was murdered.
The coroner's preliminary finding, however, reported that it's overdosed on propofol that caused Michael Jackson's death.
The Los Angeles coroner has concluded preliminarily that singer Michael Jackson died of an overdose of propofol, a powerful sedative he was given to help him sleep, according to court documents released Monday.
Los Angeles coroner Dr. Lakshmanan Sathyavagiswaran reached that preliminary conclusion after reviewing toxicology results carried out on Jackson's blood, according to a search warrant and affidavit unsealed in Houston, Texas.[Source]
There's also this report that the L.A. County Coroner ruled Michael Jackson's death a homicide. If that is the case, charges may be filed against Dr. Conrad Murray, a Las Vegas cardiologist who became Jackson’s personal physician, who administered 25 mg of propofol to Michael Jackson after repeated demands of the singer.