An ad hoc group of Prince fans is gathering signatures on a petition they plan to present next month to state and federal law enforcement demanding a grand jury investigation into the musician’s death from an accidental overdose of painkillers in April 2016.

State and federal authorities concluded their investigation this year without issuing any charges.

The petition notes that Dr. Michael Schulenberg, who had prescribed a painkiller for Prince under the name of one the musician’s friends, agreed to pay a $30,000 civil settlement with the U.S. Attorney’s Office in Minnesota.

Prince died of an overdose of fentanyl, which is not the drug that Schulenberg had prescribed.

Law enforcement was unable to determine where Prince got the drug that killed him. The petition criticizes the investigation by state and federal authorities and suggests that a grand jury would be able to “properly investigate his death.”