Kennewick — Officials must wait for lab tests to learn why an inmate died at the Benton County jail on Wednesday.

Jail staff found Robyn Montgomery Million, 58, unconscious in a housing unit while conducting a security check. She died a short time later after staff and medical personnel attempted to revive her.

Benton County Coroner John Hansens said the autopsy did not show a definitive cause of death. Lab tests will take six to eight weeks.

Sheriff’s officials said Million, who was in jail on a parole violation, had a history of drug use, and they believe she died of “natural causes.”

Sheriff Steve Keane asked the Special Investigative Unit of detectives from other police agencies to do an independent investigation of Million’s death to avoid any conflict of interest.