MINNEAPOLIS (AP) — It's been nearly a year since Prince died from an accidental drug overdose at his suburban Minneapolis estate, yet investigators still haven't interviewed a key associate or asked a grand jury to consider whether criminal charges are warranted, according to an official with knowledge of the investigation.

Prince was 57 when he was found alone and unresponsive in an elevator at his Paisley Park home on April 21. Authorities later said he died of an overdose of fentanyl, a powerful synthetic drug.

A court document says a doctor prescribed oxycodone for Prince under the name of the musician's friend to protect his privacy.

According to search warrants unsealed Monday, authorities searched Paisley Park, cellphone records of Prince's associates, and Prince's emails to try to determine where he got the fentanyl that killed him.

The documents suggest Prince was struggling with prescription opioid addiction.

One affidavit says Dr. Michael Todd Schulenberg admitted he prescribed oxycodone for Prince in a Prince's associate's name "for Prince's privacy."