(Reuters) -Eight months after Dexter Wade was struck and killed by an off-duty officer in a police vehicle in Mississippi and buried without his family's knowledge, mourners gathered on Monday for the belated funeral of the 37-year-old Black man.

Rev. Al Sharpton called Wade's death "a national outrage" in an impassioned eulogy delivered over the casket at New Horizon Church International in Jackson, Mississippi, to the applause and shouts of mourners.

More than eight months after Wade's mother reported him missing to Jackson police, Wade's body was exhumed last week after local authorities buried him in an unmarked grave in a potter's field near a Hinds County jail.

"If you think you can put him on a shelf and bury him in a potter's field like he didn't exist and we wouldn't do nothing about it, you were sadly mistaken," Sharpton said in the eulogy. "His life mattered to his mama, to his daughters, and we will make it matter all over the country."

"When this battle started, I started by myself,” Wade’s mother, Bettersten Wade said, thanking the crowded church for their donations for the funeral. "And now I ask everybody, just keep fighting with me, because it’s not over yet."

Wade was killed on the night of March 5 as he attempted to walk across an interstate highway in Jackson. The coroner's office identified him from a prescription bottle with Wade's name on it found in his pocket, according to the family and media reports. Bettersten Wade filed a missing person report a week after he disappeared and made many calls to local authorities after, Sharpton's office said.

"Bettersten wouldn't find out her son was dead and buried in an unmarked grave until this fall, at which point she paid a $250 fee to reclaim his body," Sharpton's office said in a statement.

Sharpton has joined Wade's family in calling on the U.S. Department of Justice to open a federal investigation into Wade's killing.

"I'll be here until we see the prosecution of everyone involved in the death of Dexter Wade," Sharpton said.

The coroner's office said an investigator attempted to call Wade's mother and could not get through, and then passed the information to the Jackson Police Department so it could notify Wade's next of kin of his death, NBC News reported.

Jackson Mayor Chokwe Antar Lumumba last month said the delay in notifying Wade's family "was an unfortunate and tragic accident."

(Reporting by Jonathan Allen in New York; Editing by Aurora Ellis)