The Oklahoma State Bureau of Investigation announced on Monday that it is opening a formal inquiry into the sheriff’s office that oversaw Robert C. Bates, the 73-year-old reserve deputy who shot and killed Eric Harris in April, the Associated Press reports.

Since the shooting, the Tulsa County Sheriff’s Office has been accused of misconduct over the supervision of Bates, who claims he meant to fire his Taser at Harris and inadvertently drew his gun.