(CNN) -- Opioid painkillers -- some in prescription bottles with the name Kirk Johnson on them -- were found in several places in Paisley Park following Prince's death last year, court documents unsealed Monday showed.
Dr. Michael Todd Schulenberg said he wrote an Oxycodone prescription for Prince under the name of Johnson, the singer's estate manager and longtime friend, for privacy purposes, according to a search warrant that was among the documents unsealed.
No one has been charged in connection with the superstar's death, but the details from the search warrants are beginning to show a clearer picture of the likely focus of the investigation -- which authorities say is still open and active.
The circumstances that led up to his death remain a mystery. 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? And how long was he taking opioid pain medication?
According to a search warrant issued April 21, 2016, the same day Prince was found dead in his home in Chanhassen, Minnesota, investigators found several pills labeled "Watson 853" -- hydrocodone-acetaminophen, sometimes called Vicodin -- and capsules marked "A-349," which is Percocet, in different bottles in the residence. Also according to the search warrant, investigators were told by witnesses that Prince "recently had a history of going through withdrawals which are believed to be the result of abuse of prescription medication."
Schulenberg was among those who arrived at Paisley Park after the singer's body was found in an elevator inside the complex, according to the documents.
The medical examiner's office said Prince's death was the result of an accidental overdose of the opioid fentanyl. Last August, the Minneapolis Star Tribune quoted a source with knowledge of the investigation as saying that pills seized inside the compound by investigators were labeled as hydrocodone but actually contained fentanyl.
Authorities have said the investigation into Prince's death is criminal in nature. Federal prosecutors and the Drug Enforcement Administration are investigating how Prince obtained prescription medications and from whom.
Pills found in suitcase
Information in the warrants also revealed that investigators found a suitcase containing several prescription bottles in the name of Johnson, who told investigators last year that the singer had been struggling with opiate use.
The suitcase also contained the lyrics for "You got the Look," which appeared to be in Prince's handwriting. The suitcase had a tag on it bearing the name "Peter Bravestrong," which investigators say could be an alias for Prince.
CNN's attempts to reach Johnson on Monday were not immediately successful.
About a week before his death, Prince's private jet made an emergency landing early April 15 in Moline, Illinois, on the way back from a performance in Atlanta. His publicist reassured fans that the 57-year-old star was fine, but a May 6 search warrant said investigators spoke to a witness who said Prince was rushed to a hospital because he was unconscious, and that the singer had admitted to taking one or two pain pills. Schulenberg, his doctor, was among those on the plane, according to a search warrant.
The day before Prince died, his team called an eminent opioid addiction specialist in California seeking urgent help for the singer, an attorney working for the specialist and his son said.
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.
But by the time Andrew Kornfeld arrived at the singer's Paisley Park complex on the morning of April 21, it was too late. He and two Prince representatives found the 57-year-old entertainer unresponsive in an elevator. Andrew Kornfeld was the person who called 911, Mauzy said.
CNN's Alanne Orjoux contributed to this report.