– Prosecutors charged a reserve sheriff's deputy with manslaughter Monday in the death of a man who was fatally shot as he lay on the ground at the officer's feet — a shooting that was certain to raise questions about the use of volunteer officers to supplement full-time police.

The Tulsa County Sheriff's Office has said Robert Bates, a 73-year-old insurance executive who was volunteering on an undercover operation in Tulsa, mistakenly pulled out his handgun instead of his stun gun and shot the suspect as he struggled with deputies.

Bates, who is white, was charged with second-degree manslaughter involving "culpable negligence" for the April 2 death of Eric Harris, a 44-year-old black man. If convicted, Bates could face up to four years in prison.

It was the latest fatal shooting by a police officer to draw national attention after months of investigations and protests of other deaths in North Charleston, S.C., Ferguson, Mo., New York City and Los Angeles.

A video of the incident shot by a deputy with a sunglass camera and released Friday at the request of the victim's family, shows a deputy chase and tackle Harris, whom they said tried to sell an illegal gun to an undercover officer.

As the deputy subdues Harris on the ground, a gunshot rings out and a man says: "Oh, I shot him. I'm sorry."

Harris screams: "He shot me. Oh, my God," and a ­deputy replies: "You [expletive] ran. Shut the [expletive] up."

When Harris says he's losing his breath, a deputy replies, "[Expletive] your breath."

Harris was treated by medics at the scene and died in a Tulsa hospital.

The family said in a statement that it was "saddened, shocked, confused and disturbed."

"Perhaps the most disturbing aspect of all of this is the inhumane and malicious treatment of Eric after he was shot," the family wrote. "These deputies treated Eric as less than human. They treated Eric as if his life had no value."

At a news conference on Monday, Andre Harris, the victim's brother, said he does not believe the shooting was racially motivated.

Tulsa Police Sgt. Jim Clark, who investigated the shooting as an independent consultant at the request of the sheriff, concluded that Bates had been so engrossed in the stress of the moment that he did not think clearly about what he had in his hand.

The use of reserve officers is commonplace across Oklahoma and much of the nation. Cities and counties often turn to them for extra manpower because of a lack of resources and tight budgets. They are sometimes used to free up regular officers to concentrate on high-priority duties.

Reserve deputies are permitted to carry firearms but have far less training than regular officers. About 4,000 reserve officers are active in Oklahoma. Most are unpaid and volunteer out of a sense of civic duty, officials say.

Associated Press