The probe included searches of Prince's computer, cellphone records of his friends and interviews with his associates.
The search warrants, made public Monday morning, show more than 100 white capsules labeled Watson 853 were hidden in Aleve and Bayer Aspirin bottles and found in numerous rooms inside Paisley Park.
DOCTOR TRIED TO PROTECT PRINCE'S PRIVACY: Carver County investigators and the DEA learned that Prince had no prescriptions issued to him and that Kirk Johnson had only one, oxycodone, which was prescribed on April 14 by Dr. Schulenberg, the same doctor who was at the scene of Paisley Park the day Prince died.
June 2, 2016: The Midwest Medical Examiner's Office releases a report that says Prince died from an accidental, self-administered overdose of the powerful drug fentanyl.
Criminal justice experts say the pace of the investigation doesn't necessarily mean it's in trouble or that no one will ever be charged.
Hydrocodone and acetaminophen were found in different bottles in the residence.
Fentanyl is the strongest painkiller on the market, estimated to be at least 50 times more potent than morphine and at least 30 times more potent than heroin. His death shocked fans and led to tributes worldwide. Among the unanswered questions haunting those who loved and admired him: Who supplied Prince with the painkiller that killed him? Did he know what he was taking?
PRINCE DIDN'T HAVE ANY PRESCRIPTIONS: According to the court documents, Prince didn't have a prescription for any of the drugs found at Paisley Park. There are two likely possibilities: Either a pharmaceutical manufacturer mislabeled the pills, or the pills were illegally manufactured and obtained illegally.
The long-awaited search warrants in Prince's death have been unsealed, revealing a lengthy list of prescription medications found throughout the singer's estate, some in the name of one of his oldest confidants - and several containing controlled substances. "You know, your joints get, you know, hurt".
Some of the drugs in Prince's bedroom were in a suitcase with the name Peter Bravestrong on it - believed to be an alias he used when travelling.
Johnson's lawyer did not return calls for comment on Monday.
Schulenburg is a local doctor who was employed at North Memorial Medical Center.
Judith was with Prince just days before his death.
He was found unresponsive in an elevator at Paisley Park, his home and recording studio in Chanhassen, Minnesota. Prince admitted that he had taken painkillers, according to search warrants.
Just six days before he died, Prince fell ill on a plane and made an emergency stop in IL as he returned from a gig in Atlanta.
Investigators spoke with one of Prince's previous bodyguards who said the singer was very untrusting of cell phones, after his cell phone was hacked and his personal information was stolen.
The specialist, Dr. Howard Kornfeld, couldn't get there immediately so he sent his son, Andrew Kornfeld, on an overnight flight to Minnesota. The goal was for the younger Kornfeld to help evaluate Prince's health and encourage him to enter treatment for pain management and potential addiction issues, attorney William Mauzy told reporters. Kornfeld heard a scream, and ran to see Prince lying on his side in the elevator.
Paisley Park is scheduled to host four days of concerts, tours and other events beginning on Thursday, for the one-year anniversary of Prince's death.