Prince's Death Investigated as Possible Drug Overdose: Report

law enforcement official told The Associated Press the news Thursday and said they are also looking into whether a doctor was prescribing the singer drugs prior to his death.

Sources told PEOPLE in this week's cover story that the "Purple Rain" singer had a history of using the prescription painkiller Percocet.

Officials have told AP that investigators are also looking into whether a doctor was onboard Prince's plane when it made an emergency landing in Moline, Illinois.

An autopsy of Prince's body was conducted just one day after he was found unresponsive in an elevator at his famed Paisley Park estate outside Minneapolis. While the medical examiner found "no obvious signs of trauma," toxicology reports may take weeks to complete.

On Wednesday NBC reported that the county sheriff investigating Prince's death is now asking the Drug Enforcement Administration to help with the investigation.

Other sources have told PEOPLE that Prince had also been struggling with an "ongoing illness" at the time of his shocking death – just under one week after his private plane made an emergency landing so that he could be rushed – unresponsive – to the hospital to receive what several reports called a "save shot."