The Los Angeles Coroner's office said Friday a preliminary autopsy on Jackson was inconclusive and a final cause of death would not be known until exhaustive toxicology tests are completed in "six to eight weeks."
Jackson's body was released to his family under cover of darkness late Friday, and was being kept at an undisclosed location, officials said.
Coroners investigator Steve Elias confirmed Saturday the family had informed officials they would hold a second autopsy. The TMZ.com celebrity news website said the examination was already underway.
Earlier veteran US politician and activist Reverend Jesse Jackson -- who is not related to the family -- told ABC television's Good Morning America that he had spent Friday counseling the family at their estate.
And he revealed that family members were angered by questions surrounding Jackson's death, and were focusing their attention on the role of the singer's doctor, identified as Conrad Murray.
The doctor is reported to have injected Jackson with the painkiller Demerol shortly before his death.
Reports said Los Angeles police were due to interview Murray on Saturday in the presence of a lawyer but detectives have said they do not view the physician as a criminal suspect. A lawyer representing Murray, Matt Alford, was quoted by TMZ.com as saying the doctor would meet police at 4:00 pm (2300 GMT).
"It's a human tragedy and he's upset about the death of Mr Jackson," Alford told CNN referring to Murray. "He's not a suspect in the death of Mr Jackson."
Alford said he had no knowledge of any treatments given to Jackson by Murray before the star died.
However Jesse Jackson said the family had questions of their own.
"They (the family) are suspicious of this doctor and they have real reason to be because any other doctor would say 'Here's what happened in the last hour of his life and I was there. I gave him some medicine.'
"He owes it to the family and to the public to say, 'These were the last hours of Michael's life and here's what happened.' That's a reasonable expectation."
Los Angeles coroners have said Friday's preliminary investigation showed no evidence of "external trauma or foul play."
However friends and associates of Jackson took to the airwaves to voice anger over the role of advisers and physicians that surrounded the star.
New age guru and Jackson confidante Deepak Chopra -- a qualified cardiologist -- told CNN bluntly: "I think drugs killed him."
Anger was also beginning to be seen amongst fans who have gathered around the globe in their thousands to pay tribute to Jackson.
On the Hollywood Walk of Fame in Los Angeles, fans queued again on Saturday for the right to file past Jackson's star set in the sidewalk.
Deborah Canton, 46, sobbed inconsolably as she slammed the "evil people" who she accused of driving Jackson to his death.
"The guy would never hurt a fly but all of these evil people would do everything to destroy him just to get his money," she said. "I don't think he wanted to live anymore."
In New York large crowds formed outside the legendary Apollo Theater in Harlem, where Jackson launched his career in 1969.
Meanwhile revelers at Britain's Glastonbury music festival sported T-shirts with slogans like "Michael Jackson RIP" and "I was at Glasto when Jacko died", while graffiti paying tribute to "The King of Pop" adorned tents.
Jackson's death has sent fans scrambling to stock up on his music, and British chart officials said a compilation album was likely to go to the top of the charts on Sunday.
"We always find where a great icon dies that there's a massive uplift in their music sales as fans want to connect and express their grief through the records," said Gennaro Castaldo of retailer HMV.
While Jackson ruled the charts and dazzled audiences with dance moves like the "moonwalk" in the 1980s, his once-stellar career was overshadowed by his startling physical transformation and multiple allegations of child abuse.
He lived as a virtual recluse following his 2005 acquittal on charges of child molestation and plotting to kidnap his young accuser.
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