Michael Jackson's personal physician DR. Conrad Murray has refused to testify in a wrongful death lawsuit filed by the superstar's mother against concert promoters Aeg Live.

Katherine Jackson is holding promoters behind her son's doomed This Is It comeback shows responsible for the King of Pop's death, claiming they were negligent in ignoring life-threatening health concerns going on behind closed doors.

Her lawyers had reportedly prepared to depose Murray during a prison visit on Monday (18Mar13), but the trip was cancelled after the medic, who is serving four years for involuntary manslaughter relating to the singer's 2009 death, insisted he would not participate and would use the U.S. Constitution's Fifth Amendment to avoid incriminating himself.

He made his feelings clear in a signed, sworn statement addressed to the Jacksons, and Katherine's lawyer, Kevin Boyle, confirms to CNN.com, "He would not answer any questions at the deposition or the trial."

Murray, who has maintained his innocence in Jackson's death, also refused to take the stand and share his side of the story during his own trial in 2011.

The Jackson matriarch is demanding a massive $40 billion from Aeg bosses, who she accuses of negligently hiring and supervising Murray.

The case is due to go to trail on 2 April (13).