Officials investigating the death of music icon Michael Jackson are looking at the King of Pop’s past struggles with prescription-drug addiction to help determine if his death was due to an overdose, the Chicago Tribune reported June 27.

Craig Harvey, a spokesman for the Los Angeles County Coroner’s Office, confirmed that Jackson was taking some form of prescription medication. The coroner will have to perform tests, including a toxicology screen, over the next four to six weeks in order to determine Jackson’s cause of death, Harvey said.

Detectives interviewed Conrad Murray, a cardiologist who was at Jackson’s home last Thursday when the singer went into cardiac arrest. According to one of Jackson’s advisers, Murray was Jackson’s personal doctor for three years, and his main job was to keep Jackson healthy as he prepared for a comeback concert series next month in London.

Jackson previously acknowledged an addiction to prescription drugs in the 1990s.

Police seized Murray’s car last week. “It may contain medications or other evidence that may assist the coroner in determining the cause of death,” a police spokeswoman said.

Jackson passed a four-hour physical exam this past spring to insure his London performances. Jackson’s concert promoter, Randy Phillips, said the exam would have determined whether Jackson was using prescription drugs.