Investigative journalist Diane Dimond tells ET's Mary Hart that this isn't the first time that Dr. Conrad Murray, the doctor who was at Michael Jackson's home the day the King of Pop went into cardiac arrest, has undergone scrutiny.

Diane tells Mary that the Las Vegas Coroner's office investigated the death of one of Dr. Murray's patients in 2007.

"When the patient died after surgery, his wife complained to the coroner, who found that a puncture wound to the heart contributed to the man's death," Diane says.

Dr. Murray faced no malpractice suit in the death. His attorney told ET that his client's record is clean.

Sources also tell Diane that a lawsuit may be looming over the Tuesday memorial service at the Staples Center in Los Angeles, and that Joe Jackson may be filing it.

The target is AEG, the company that oversaw the public tribute and was producing Michael's 50 comeback concerts. AEG has not responded yet to ET.

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