A family attorney said on Friday he had been concerned that Jackson's use of prescription drugs for dancing-related injuries would eventually prove fatal and that the entertainer's inner circle had ignored his warnings.
Authorities scheduled an autopsy for Friday. But they cautioned it could take weeks to determine a cause of death, which will likely have to wait for the return of toxicology tests. Those tests will determine if Jackson had any drugs, alcohol or prescription medications in his system.
Jackson, a former child star who became one of the best-selling pop artists of all time before descending into a strange and reclusive lifestyle amid accusations of child molestation, died Thursday afternoon at a Los Angeles hospital. He had been rushed to the hospital in full cardiac arrest after collapsing at his nearby rental home.
Jackson's passing was front-page news around the world as airwaves filled with his greatest hits from "Thriller" to "Billie Jean" and social networking sites were bombarded with messages and tributes from fans and musicians.
"It's so sad and shocking," former Beatle Paul McCartney said. "I feel privileged to have hung out and worked with Michael. He was a massively talented boy man with a gentle soul. His music will be remembered forever."
Few details were known about the circumstances surrounding Jackson's death but he was reportedly unconscious and not breathing by the time he arrived at UCLA Medical Center. Doctors were unable to revive him.
His body was flown by helicopter from the hospital to the coroner's office late Thursday.
Lawyer Brian Oxman, a spokesman for the Jackson family, told CBS's "The Early Show" on Friday that he had been concerned about the prescription drugs that Jackson took due to injuries suffered while performing.
"I had warned everyone that I could warn and I told them that one day, Michael Jackson is going to wake up dead, which is a very odd way of putting it ...," Oxman said. "I do not want to point fingers at anyone because I want to hear what the toxicology report says and the coroner says but the plain fact of the matter is that Michael Jackson had prescription drugs at his disposal at all times.
Detectives from the Los Angeles Police Department's Robbery Homicide division searched Jackson's home in the upscale Holmby Hills neighborhood of Los Angeles at the behest of Chief William Bratton. But they called the investigation an "everyday" event.
Facing a battered reputation and a mountain of debts which The Wall Street Journal reported ran to $500 million, Jackson had spent the last two months rehearsing for the London concerts, including Wednesday night at the huge Staples Center arena, home to the Los Angeles Lakers basketball team.
In death, his music enjoyed a commercial renaissance that had eluded him for years. His songs surged to the top 15 slots on online retailer Amazon.com Inc's best-selling albums within hours.
Jackson dominated the charts in the 1980s and is considered one of the most successful entertainers of the past century, with a lifetime sales tally estimated at 750 million records, 13 Grammy Awards and several seminal music videos to his name.
"Michael was and will remain one of the greatest entertainers that ever lived," said Motown Records founder Berry Gordy, Jackson's first label boss. "He was exceptional, artistic and original. He gave the world his heart and soul through his music."
Jackson's reputation as a singer and dancer was overshadowed in recent years by his increasingly abnormal appearance and bizarre lifestyle, which included his friendship with a chimp and a preference for the company of children.
He named his estate in the central California foothills Neverland Valley Ranch, in tribute to the J.M. Barrie's Peter Pan stories, and filled it with amusement park rides and a petting zoo.
Jackson was twice accused of molesting young boys and was charged in 2003 with child sexual abuse. He became even more reclusive following his 2005 acquittal and vowed he would never again live at Neverland.
Despite reports of Jackson's ill health, the promoters of the London shows, AEG Live, said in March that Jackson passed a 4-1/2 hour physical examination with independent doctors.
"I can't stop crying over the sad news," pop star Madonna said in a statement. "I have always admired Michael Jackson. The world has lost one of the greats but his music will live on forever."
Jackson was born on Aug. 29, 1958, in Gary, Indiana, the seventh of nine children and first performed with his brothers as a member of the Jackson 5.
His 1982 album "Thriller" yielded seven top-10 singles. The album sold 21 million copies in the United States and at least 27 million internationally.
The following year, he unveiled his signature "moonwalk" dance move, gliding across the stage and setting off an instant trend, while performing "Billie Jean" during an NBC special.
In 1994, Jackson married Elvis Presley's only child, Lisa Marie, but the marriage ended in divorce in 1996.
"I'm so very sad and confused with every emotion possible. ... This is such a massive loss on so many levels, words fail me," Presley said in statement.
Jackson married Debbie Rowe the same year and had two children, before splitting in 1999, and he later had another child with an unidentified surrogate mother.
He is survived by three children named Prince Michael I, Paris Michael and Prince Michael II, known for his brief public appearance when his father held him over the railing of a hotel balcony, causing widespread criticism.
(Editing by Bill Trott and Howard Goller)