Detective Orlando Martinez, who was to testify briefly Wednesday, told jurors in California Superior Court in Los Angeles Tuesday that when he started investigating Jackson's death in 2009, he first thought the cause of death was accidental or natural, based on Murray's statements.
But when Martinez learned of Murray's deep financial straits from public records, he shifted his thinking to consider the pop star's death was motivated by Murray's desire for "financial gain," he said.
The doctor owed hundreds of thousands of dollars in tax liens, child support and other debts, and had closed his office to work with Jackson and Jackson alone, tying his financial future to him, Martinez said.
Murray appears to have done whatever he felt he needed to do to get the $150,000 a month he expected to be paid by Jackson promoter Anschutz Entertainment Group Live, Martinez said.
"He may break the rules, bend the rules, do whatever he needed to do to get paid," Martinez said. "It might solve his money problems."
Murray, who is not involved in the wrongful-death lawsuit, was convicted of involuntary manslaughter in 2011 for giving Jackson a fatal dose of the anesthetic propofol to help him sleep. He is completing a four-year prison sentence.
Jackson's 82-year-old mother, Katherine -- who is also the legal guardian of Jackson's children Prince, Paris and Blanket -- is suing AEG Live for the pop singer's wrongful death.
AEG Live sponsored a planned series of 50 Jackson "This Is It" comeback concerts that were to be held at London's O2 Arena from July 2009 through March 2010.
Jackson died June 25, 2009, at age 50, less than three weeks before the first scheduled concert July 13.
The lawsuit alleges AEG Live was negligent in hiring Murray to care for the singer while he rehearsed for the concerts.
AEG Live lawyers argue Jackson was treated by Murray before the shows were even planned. They say Jackson chose and controlled Murray and was addicted to prescription drugs long before he agreed to do the concerts.
Katherine Jackson, who filed the wrongful-death lawsuit after Murray's conviction, seeks damages of equivalent to the amount of money Jackson would have earned over the course of his remaining lifetime if he had not died in 2009, estimated at $40 billion.
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