Even though the shock of the King of Pop's death is still fresh, news reports are beginning to emerge as to what caused the cardiac arrest that ended Michael Jackson's life at just 50 years old. Last night, the rarely trustworthy U.K. tabloid the Sun reported that "an Emergency Room source at UCLA hospital said Jackson aides told medics he had collapsed after an injection of potent Demerol," a report that TMZ just seconded after speaking to "a close member of Michael Jackson's family." People is also reporting that associates of Jackson's who were helping him prep for his upcoming residency at London's O2 arena were alarmed by his "unavoidably thin and fragile" body. Perhaps most telling, the New York Post has posted a story saying that authorities have been unable to locate Jackson's personal physician, Dr. Conrad Robert Murray, and fear that he has "gone missing." Developing ...

UPDATE: Dr. Conrad Robert Murray has been located and is preparing to speak with the authorities.