An intitial autopsy report has found the cause of George Michael's death "inconclusive," Thomas Valley Police wrote in a statement Friday.
Officials must carry out further tests to find out how the 53-year-old died on Christmas Day at his home in the U.K. The results of the investigation are not expected to be known for several weeks, officials say.
"Thames Valley Police will prepare a file for the Oxfordshire Coroner. Mr Michael's death is still being treated as unexplained but not suspicious," the police department wrote.
Early reports on the former Wham! singer's death state that he died of heart failure. More details on his health history have been publicized in the past. Although there has been no official connection made between drugs and his death, the singer had worked through substance abuse issues over the years.
In an interview with The Guardian in 2009, he revealed having previous problems with using sleeping pills and that he had smoked crack cocaine before. Michael also shared that he had been making some sense of his addictions.
"People want to see me as tragic with all the cottaging and drug-taking... those things are not what most people aspire to, and I think it removes people's envy to see your weaknesses," he said. "I don't even see them as weaknesses any more. It's just who I am."
In the next several days, fans who have turned the outside of Michael's home into a memorial, will continue mourning his death. A date for Michael's funeral has not been announced yet, but longtime friend Elton John is reportedly planning a memorial service for him.