(CNN) — The focus of the investigation into the death of Prince appeared to be shifting Wednesday to the role of a Minnesota doctor revealed in a search warrant to have seen the entertainer twice in the weeks before his death.

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 the day the singer died, apparently to deliver test results.

The search warrant documents published by the newspapers 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.

Investigators have been looking into the cause of the 57-year-old singer’s April 21 death. Results of an April 22 autopsy are pending.

According to a law enforcement source, investigators found prescription opioid medication on Prince and at Paisley Park after his death. It’s unclear if he was being treated for any health issues.

Federal agents have joined the investigation in an effort to determine if people in Prince’s inner circle may have helped obtain drugs for him, law enforcement officials familiar with the investigation told CNN last week.

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 the singer’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.

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 Drug Enforcement Administration 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.

CNN’s Emanuella Grinberg contributed to this report.