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 is certain to raise questions about the use of volunteer officers to supplement full-time police.

The sheriff’s office has said Robert Bates, a 73-year-old insurance executive who was volunteering on an undercover operation in Tulsa, mistakenly pulled 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, he 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 Ferguson, Mo., New York City, Los Angeles and other elsewhere.

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

As the deputy subdued Harris, a gunshot rang out and a man is heard to say, “Oh, I shot him. I’m sorry.”

Harris screamed, “He shot me. Oh, my God,” and a deputy replied, “You f—-ing ran. Shut the f—- up.”

When Harris said he was losing his breath, a deputy replied, “F—- 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.”

Oklahoma law defines culpable negligence as “the omission to do something which a reasonably careful person would do, or the lack of the usual ordinary care and caution in the performance of an act usually and ordinarily exercised by a person under similar circumstances and conditions,” Tulsa County District Attorney Steve Kunzweiler said in a statement.

Reserve deputies are permitted to carry firearms but have far less training than regular officers.

About 4,000 reserve officers are active in Oklahoma, according to the Council on Law Enforcement Education and Training. Most are unpaid and volunteer simply out of a sense of civic duty, said council Director Steve Emmons.

The Oklahoma chapter of the American Civil Liberties Union called Monday for an end to the use of reserve officers for significant police work.

“There are lots of legitimate functions for those reserve officers, like helping out in national disasters or putting up sandbags during flooding,” said the chapter’s executive director, Ryan Kiesel. “But under no circumstances should we be arming people who essentially want to play a grown-up version of police officer with deadly consequences.”