The veteran politician, who has been counselling the family, said they were upset the official cause of death might not be known for weeks.
He said the family wanted answers from the star's personal doctor, Conrad Murray, who was with him when he died, reports The BBC.
Los Angeles County medical examiners completed an autopsy Friday and said Jackson had taken prescription medication.
Medical officials also said there was no indication of trauma or foul play. An official cause of death could take weeks.
In a statement issued by his father Joseph Jackson, the star''s relatives called it "one of the darkest moments of our lives".
"It leaves us, his family, speechless and devastated to a point where communication with the outside world seems almost impossible at times," the statement said.