A group of Prince fans on Tuesday asked the U.S. Attorney's Office in Minnesota to open a grand jury investigation into the rock star's death.

Federal, state and county law enforcement officers spent almost two years investigating Prince's accidental fatal overdose but were not able to trace the source of the painkiller that killed him in April 2016.

"We want justice to be served," said Nicole Welage, one of more than a dozen Prince fans who pushed to petition for a federal grand jury investigation.

The U.S. Attorney's Office declined Tuesday to comment on the petition. Earlier this year, officials there said prosecutors found "no credible evidence" that would lead to federal criminal charges. The case is now considered inactive.

Welage said she and other fans poured through 214 pages of investigative documents along with the transcript of the 911 call made to authorities after Prince was found in his Paisley Park home. More answers are needed, she said.

The petition, signed by more than 6,000 Prince fans, suggests a grand jury would "properly investigate his death." The fans also delivered their petition to local and state officials.

The person who supplied the drug to Prince needs to be held accountable, Welage said.

"He led a clean life, and he's being completely painted as a drug overdose — another Elvis," she said. "We don't believe that's what happened."

Mary Lynn Smith