"Not just one person was involved, rather it was a conspiracy of people. He was surrounded by a bad circle. Michael was a very meek, quiet, loving person. People took advantage of that.
"Less than a month ago, I said I thought Michael was going to die before the London shows because he was surrounded by people who didn't have his best interests at heart.
La Toya said she had ordered a private autopsy.
Jackson, one of the world's most popular entertainers, died on June 25 at the age of 50.
"Michael was worth more than a billion dollars. When anyone is worth that much money, there are always greedy people around them. I said to my family a month ago, 'He's never going to make it to London'. He was worth more dead than alive."
Murder under Californian law can include killings that are not premeditated.
La Toya accused a "shadowy" group of cutting her sibling off from his family and friends and forcing him to sign up for 50 comeback concerts at London's O2 Arena, shows billed "This Is It".
They saw him as a "cash cow" and "got him hooked on drugs... I think it shocked his system so much it killed him," she claimed.
"I am not going to stop until I find out who is responsible. Why did they keep the family away? It's not about money. I want justice for Michael. I won't rest until I find out what -- and who -- killed my brother."
La Toya said Jackson was found in the bedroom of his physician Doctor Conrad Murray.
"Michael walked from his room to Doctor Murray's room. What happened in there we don't know," she said.
La Toya said she was driving to see Jackson in hospital when her mother screamed down the phone: "He's dead!".
"I nearly crashed my car," she said. "My legs went weak... They took me up to the area where Michael had been taken. Mother was crying and Michael's kids were crying."
She also claimed jewellery was missing from his house and no cash was found, despite the fact he regularly kept more than a million dollars around.
La Toya said the family had an open coffin viewing before the public memorial in Los Angeles' Staples Center arena.
She put one of his sequined gloves in the coffin, while his daughter Paris, 11, put a one half a heart-shaped "mood necklace" around his wrist, keeping the other piece.
La Toya said it was Paris's idea to speak at the memorial.
Of Jackson's children, she said Paris wanted to be an entertainer, Prince Michael was "assertive", while Blanket was "very funny, a real prankster like his father."
La Toya said her brother would "absolutely not" be laid to rest at his Neverland ranch and added that Jackson's brain, removed in the autopsy, had been put back in his body.
La Toya said Jackson wanted to give up music and become a film director.
"The first one was to be a horror film called 'Thriller'," she said. "'This Is It' really was the end. He didn't want to perform any more."
She said Jackson updated his will roughly every five years, "so we expect another one to emerge from 2007".
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