A law enforcement official tells the Associated Press that tests show Prince died of an opioid overdose.
The official, who is close to the investigation, spoke on condition of anonymity because he was not authorized to speak to the media.
A search warrant in May revealed that Dr. Michael Todd Schulenberg, 46, treated Prince on April 7 and April 20 and prescribed him medications, though it didn't specify the drugs or say whether Prince took them. Prince was found dead April 21 in his suburban Minneapolis home.
That month, a law enforcement official told the Associated Press that investigators were looking into whether Prince died from an overdose and whether a doctor was prescribing him drugs in the weeks before his death.
Investigators interviewed Schulenberg and searched a suburban Minneapolis hospital where he worked, according to the warrant.
On May 4, a spokesperson for the US Attorney's Office announced that the US Attorney's Office in Minnesota and the DEA officially joined the Carver County Sheriff's investigation into who may have provided the prescription pills to Prince.