Robert Bates

Robert Bates, a former Oklahoma volunteer sheriff's deputy who said he mistook his handgun for his stun gun when he fatally shot an unarmed suspect in 2015, is escorted from the courtroom following his sentencing Tuesday at the courthouse in Tulsa, Okla.

(Sue Ogrocki, Associated Press)

TULSA, Oklahoma -- A former reserve deputy in Oklahoma has been sentenced to four years in prison for accidentally shooting a suspect when he mistook his handgun for a Taser.

The four-year sentence was the maximum for Robert Bates, 74, who was found guilty by a jury of second-degree manslaughter on April 27, CNN reports.

The shooting occurred on April 2, 2015, while Bates was working with the Tulsa County Sheriff's Department. Deputies conducting an illegal gun-sales sting were attempting to arrest Eric C. Harris, 44.

Harris, who was unarmed, ran from deputies and was being restrained when Bates approached, yelled "Taser", and then shot Harris in the back.

"Oh! I shot him! I'm sorry!" Bates said immediately after the shooting.

The Associated Press reports Bates' qualifications to serve as a reserve deputy had been questioned by an internal memo. It also was learned that Bates, a wealthy insurance executive, was a close friend of the sheriff and had donated cash, vehicles and equipment to the department.

Defense lawyers blamed Harris' death on methamphetamine found in his system and on poor cardiac health. They are planning to appeal the decision.

If you wish to discuss or comment on this story, please visit Tuesday's crime and courts comments section.