Six potential grand jurors called to investigate an Oklahoma sheriff and his agency were excused on Monday by a judge after they expressed concerns they couldn’t serve on the panel for personal reasons.

District judge Rebecca Nightingale met with 26 residents who expressed concerns they couldn’t serve on the jury called to investigate whether the Tulsa County sheriff, Stanley Glanz, neglected his duties and whether reserve deputies were afforded special treatment after donating to the sheriff’s office. She allowed six of those to be excused from duty.

Nightingale later released a pool of nearly 60 jurors for the day. The judge’s bailiff, Brooke Golightly, said questioning of citizens would begin on Tuesday and it was likely that the jury and alternates would be selected later in the day.

A petition drive calling for the grand jury was prompted by the fatal shooting of an unarmed man by ex-volunteer deputy Robert Bates on 2 April and a 2009 memo that was leaked weeks later, which questioned whether Bates was qualified to serve as a reserve deputy. Bates, who has since left the agency, claims he confused his handgun and stun gun when he shot Eric Harris. He has pleaded not guilty to second-degree manslaughter and will face a jury trial in February.

Bates is a close friend of Glanz’s, has donated thousands of dollars in cash, cars and equipment to the agency and was the sheriff’s campaign manager in 2012.

Glanz’s attorneys tried for weeks to stop the grand jury with court challenges, but the Oklahoma supreme court ruled last week that the investigation could proceed.

“I think it’s an exciting time for Tulsa County to see the process go forward,” said Marq Lewis, an organizer of the petition drive, which was conducted by We The People Oklahoma.

Terry Simonson, a spokesman for the sheriff, suggested the grand jury was a waste of taxpayer money, as the case is already being probed by the Oklahoma state bureau of investigation and an outside agency is reviewing the agency’s operations.

“The question is: why are taxpayers paying for this three times?” Simonson said before jury selection began.

Grand jurors will hear testimony from witnesses whose appearances are coordinated by a legal adviser assigned to the case. Both the adviser and jurors ask questions of witnesses and the panel decides when it meets and for how long. In order for an indictment or suggestion for removal from office to go forward, three-fourths of the grand jurors must recommend it.

