The Oklahoma Supreme Court said Thursday it will consider whether to stop a grand jury investigation into an embattled sheriff whose longtime friend and volunteer deputy fatally shot an unarmed man.

Attorneys for Tulsa County Sheriff Stanley Glanz want justices to toss out a lower court's decision to empanel a grand jury on July 20. The state Supreme Court late Thursday appointed a referee to hear evidence and arguments in the case on July 14.

More than 6,600 Tulsa residents petitioned for the investigation into whether Glanz neglected his duties and whether reservists who gave gifts to the sheriff were shown special treatment. Glanz's lawyers say some signatures were gathered improperly and the petition should be tossed.

District Judge Rebecca Nightingale on Tuesday rejected Glanz's claims. Terry Simonson, a spokesman for the sheriff, said Glanz is appealing to the high court because the law has been applied incorrectly.

"He has the same rights as every citizen in Oklahoma to defend the position he believes in and the right to appeal based upon that conviction," Simonson said. "That's what he did today."

The petition drive began after reserve deputy Robert Bates, 73, shot and killed Eric Harris on April 2. Harris ran from authorities during a gun-sales sting operation and Bates maintains he confused his stun gun and handgun. Bates has pleaded not guilty to second-degree manslaughter in the slaying.