The search warrant, obtained by the Los Angeles Times
and the Minneapolis Star Tribune
, also reveals Dr. Michael Schulenberg went to Prince's Paisley Park studios on April 21, the day the musician died, apparently to deliver test results.
Investigators are interested in learning more about the relationship between Schulenberg and Prince, as well as members of the musician's inner circle, law enforcement officials told CNN on Wednesday.
Authorities said they have not found a valid prescription for opioid medication, either on Prince's person or at Paisley Park. The evidence found so far doesn't suggest that Prince was "doctor shopping" -- or seeking prescriptions from multiple doctors -- as has happened in other prominent celebrity deaths, law enforcement officials said previously.
Instead, investigators are focused on the possibility that so-called "drug runners" were obtaining the medications for Prince.
It's unclear whether the singer was being treated for any health issues. Results of the autopsy are pending.
The search warrant documents
published by the newspapers show investigators sought medical records from the clinic where Schulenberg worked until Tuesday, but do not describe why the doctor was treating Prince.
In a search warrant affidavit, Carver County Sheriff's Office Detective Chris Nelson said Schulenberg had told him he had seen Prince on April 7 and again the day before his death.
He also had issued the singer a prescription to be filled at a Walgreen's store. The affidavit does not disclose what the prescription was for, however.
Amy Conners, an attorney for the doctor, told CNN: "Dr. Schulenberg is cooperating with investigators."
Schulenberg has not been accused of any wrongdoing.
Investigators have been looking into the cause of the 57-year-old artist's death. Results of an April 22 autopsy and toxicology tests are pending.
The search warrant documents obtained by the Times and Star Tribune are no longer publicly available. The documents are under seal and should not have been released, said Nancy Peters of the Hennepin County District Court.
Attorney: Siblings spoke of Percocet addiction
Last week, the former attorney for two of Prince's dead siblings says they had revealed Prince had an addiction
to Percocet decades ago.
Prince's half-brother, Duane Nelson, said he used to get the drug for Prince to help him come down after shows, attorney Michael B. Padden said. Nelson died in 2013.
Another half-sibling, Lorna Nelson, also alleged drug use by Prince, but was not involved in getting drugs for him, Padden said. She died in 2006.
Schulenberg: What we know
According to records with the Minnesota Board of Medical Practice, Schulenberg is certified in family medicine and has no criminal convictions.
He is a 1995 graduate of the Oregon Health Sciences University in Portland, Oregon, according to the records.
The clinic where Schulenberg practiced family medicine said he was no longer working there as of Tuesday. Deborah Cannon with North Memorial Clinic gave no details as to why Schulenberg was no longer employed.
CNN called several numbers listed for the doctor and left a request for comment on his voice mail. Calls and emails by CNN to his attorney were not immediately returned.
"Revisiting the scene"
The revelations accompanied fresh activity at the Paisley Park complex where Prince died.
Agents from the U.S. Drug Enforcement Administration and local sheriff's deputies were at Prince's home on Tuesday
as part of an ongoing investigation into the music legend's death, a law enforcement official told CNN.
The DEA agents were executing a federal search warrant, the source said. They were looking for additional evidence that could help explain the source of prescription opioids, sources told CNN.
CNN affiliate WCCO
reported more than a dozen vehicles were at Paisley Park.
The Carver County Sheriff's Office tweeted Tuesday that detectives were "revisiting the scene" as part of their "complete investigation."
The U.S. Attorney's Office and the DEA announced last week they were joining forces with local investigators, led by the sheriff's office in Carver County, to investigate Prince's death.
The county includes the Minneapolis suburb of Chanhassen, where Prince's Paisley Park complex is located.
Source: Opioids found at scene
Officials have yet to publicly comment on what killed Prince. But attention has increasingly focused on the possible involvement of opioid pain killers.
The day before Prince died, his team called an eminent opioid addiction specialist in California seeking urgent help for the singer
, William Mauzy, an attorney working for the specialist and his son, said last week.
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, Mauzy said.
Andrew Kornfeld called 911 after representatives of the singer discovered him unresponsive in an elevator the morning of April 21, Mauzy said.
Opioids reduce pain by switching off pain receptors in the brain.
They are among the most widely prescribed drugs in the United States, the Centers for Disease Control and Prevention says. Prescription opioids include painkillers such as morphine, oxycodone and hydrocodone, according to the CDC.
Opioids produce an increased pain tolerance and a sense of euphoria. They trigger a craving when the drug is absent.