MINNEAPOLIS — Thousands of Prince fans are asking federal authorities to open a grand jury investigation into his death.

The petition to the U.S. Attorney’s Office has been signed by more than 6,000 people. One of the petition’s organizers, Nicole Welage, says more answers are needed about the rock star’s accidental fentanyl overdose in 2016. Welage tells the Star Tribune that the person who supplied the drug must be held accountable.

Federal, state and county investigators spent nearly two years looking into Prince’s death , but were unable to trace the source of the drug that killed him .