Speculation mounted today that Michael Jackson's fatal heart attack might have been brought on by an injection of painkilling drugs after a rehearsal at a Los Angeles arena for the star's comeback concerts in London.

As thousands of fans gathered outside the Ronald Reagan UCLA Medical Center, where Jackson was pronounced dead yesterday afternoon, LAPD detectives searched the rented mansion in the Holmby Hills area of the city where the singer had been living.

Jackson's death was confirmed by his brother Jermaine in an emotional press conference at the hospital. “We believe he suffered a cardiac arrest at his home, however the cause of his death is unknown until the results of the autopsy are known," he said.

"The personal physician who was with him at the time attempted to resuscitate him.”

Times Archive 1972 The Jackson Five live at Wembley

Michael Jackson's twinkling feet scarcely seemed to touch the stage

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Paramedics were called to the Jackson home at 12.21pm local time to respond to a "50-year-old male" who was "not breathing at all". He was rushed to the UCLA hospital but doctors were unable to revive him and his death was confirmed at 2.26pm.

The star's sudden death shocked the world of music and entertainment. Elizabeth Taylor, a close friend, was said to be "devastated" while Madonna said: "I can't stop crying over the sad news."

By any reckoning, Jackson was the King of Pop, a former child star with the Jackson Five who went on to create the world's bestselling album with his 1982 release Thriller, which sold up to 57 million copies. Among those paying tributes was his ex-wife Lisa Marie Presley, whose father Elvis Presley met a drug-induced death in 1977 at the age of 42.

Ms Presley said that she was "sad and confused with every emotion possible" and "heartbroken" for the singer's three children.

Last night his body was flown by helicopter to the coroner's office and an autopsy is scheduled later today. But officials warned that it could take weeks to determine a cause of death because of the complicated toxicology tests needed to determine if Jackson had any drugs, alcohol or prescription medications in his system.

The Sun newspaper today reported that Jackson aides told medics at the UCLA emergency room that the star had collapsed after an injection of the drug Demerol, a powerful painkiller which is similar to morphine and which is known to come with the risk of cardiac arrest.

“Shortly after taking the Demerol he started to experience slow shallow breathing," the newspaper quoted one source as saying. “His breathing gradually got slower and slower until it stopped."

No confirmation was immediately available on that report, but the celebrity website TMZ said that Jackson had on Wednesday night attended a rehearsal at LA's Staples Center to prepare for the series of 50 concerts scheduled for London's O2 dome that had been due to start next month and last into next year.

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