A law enforcement official tells The Associated Press that investigators are looking into whether Prince died from a drug overdose and whether a doctor was prescribing him drugs in the weeks before his death.
The official says that among the things investigators are looking at is whether a doctor was on a plane that made an emergency landing in Illinois less than a week before Prince died.
The law enforcement official has been briefed on the investigation and spoke on condition of anonymity because he was not authorized to speak to the media
The official says investigators are also looking into what kind of drugs were on plane and at his house in suburban Minneapolis.
Prescription painkillers were found in Prince's possession when he died on April 21, according to federal law enforcement officials who spoke to NBC News.
The pop icon was found unresponsive in an elevator after they were called to Paisley Park. First responders tried CPR, but couldn't revive the 57-year-old musician, according to police.