Music legend Prince had prescription painkillers in his possession when he died, according to law enforcement officials.
NBC News also reports that painkillers were found in the singer's Minnesota residence, where he was found unresponsive April 21.
According to NBC, the Carver County sheriff is enlisting the help of the Drug Enforcement Administration in the investigation. The DEA will assist in finding out where the painkillers came from, as well as what prescriptions the singer may have had.
An autopsy on the singer was completed on Friday by the Midwest Medical Examiner, though the examiner's office said that the results could take weeks.
The singer's body was cremated, and a memorial service was held for him over the weekend.
Authorities responded to an emergency call and found the singer unresponsive in the elevator of his home, dubbed Paisley Park. Responders were unable to revive him.
According to TMZ, the singer's plane made an emergency landing in Moline, Ill., on April 15, and Prince was rushed to the hospital to be treated for an overdose of the opioid painkiller Percocet.
On Monday, the Minneapolis Star Tribune reported that a longtime attorney for two of Prince's siblings told authorities his clients told him over a decade ago that Prince had "substantial" drug problems, specifically with Percocet and cocaine.
TMZ reported Wednesday that Prince had suffered from a Percocet addiction for years, obtaining a prescription for the painkiller for hip issues in 2009. By the time the singer underwent surgery to correct the hip problem, the site reported, he had already become addicted.
According to court papers filed by Prince's sister Tyka Nelson, the "When Doves Cry" musician did not leave a will. On Wednesday, a Minnesota court appointed Bremer Trust, National Association as special administrator of the singer's estate. For a number of years, Bremer Bank, National Association had provided financial services for the singer.