Why was a 73-year-old insurance company executive playing cop?

That’s the simple question many are asking more than a week after an undercover Tulsa sheriff’s operation went wrong — and a white reserve deputy sheriff shot and killed an unarmed black man, apparently by accident.

Robert Bates' booking photo. (Tulsa County Jail) Robert Bates in his April 14 booking photo. (Tulsa County Jail)

The reserve deputy, Robert Bates, was charged Monday with second-degree manslaughter, the Tulsa County District Attorney’s Office said. Bates turned himself in on Tuesday.

[Tulsa case adds to count of police officers charged in fatal on-duty shootings]

“Mr. Bates is charged with Second-Degree Manslaughter involving culpable negligence,” Tulsa County District Attorney Steve Kunzweiler said in a statement. “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.’

“The defendant is presumed to be innocent under the law but we will be prepared to present evidence at future court hearings.”

Bates surrendered to authorities at the Tulsa County Jail on Tuesday morning, the Tulsa World reported.

He was released on $25,000 bond, according to jail records.

The family of the man who was shot, 44-year-old Eric Harris, released a statement Tuesday, calling the charge a “necessary first step on the road to justice and for our family’s healing process.”

“At the same time, we know that there is a long road ahead,” the statement read. “There remain many unanswered questions. And we will continue to fight until those questions are answered. We will continue to fight until justice is realized.”

If convicted, Bates could face a maximum of four years in prison and a fine that wouldn’t exceed $1,000, according to the district attorney’s office.

“I frankly think they shouldn’t have been filed. It was an excusable homicide, in my opinion,” Bates’ attorney, Clark Brewster, told News On 6. “The circumstances were not intentional. It was an accident.”

[Thousands of police shootings since 2005 result in few prosecutions]

A Tulsa County Sheriff’s Office public information officer declined to offer additional comment after Bates was charged Monday.

When Bates pulled his weapon and shot Harris on April 2, he said he thought his handgun was his Taser. In a video released by police over the weekend, a gunshot fires and Bates says, “Oh, I shot him. I’m sorry.” It was one of at least two shootings this month in which a white officer shot and killed an unarmed black man — and it has created a backlash for many reasons, one being Bates is not a real police officer. He’s a reserve sheriff’s deputy. And some fear he wasn’t qualified to be one.

[Why an officer’s expletive is more shocking to people than watching Eric Harris die]

The Tulsa World said Bates, who worked for a year as a police officer in 1964-65, served as chairman of the Re-elect Sheriff (Stanley) Glanz Committee in 2012 and donated $2,500 to Glanz’s campaign that year. The footage of the shooting was captured on another deputy’s body camera.

What was a reserve cop, aging or otherwise, doing with a weapon?

Editor's note: This video contains graphic content. The Tulsa County Sheriff's Office released video of the undercover operation involving a 44-year-old unarmed black man, Eric Harris, that took place before he was fatally shot by a reserve deputy on Apr. 2. (Tulsa County Sheriff's Office via Tulsa World)

It’s not all that uncommon. Volunteer reserve officers have become a staple in the Tulsa sheriff’s department, which reportedly uses about 100 of them, as well as in many other cities. It’s not unusual for them to be out on assignment, Tulsa County Sheriff’s Maj. Shannon Clark told the Tulsa World. By trade, they’re bankers, doctors, lawyers, retired cops or even celebrities. They get varying degrees of training and they help the local police, not just by patrolling with them, usually at no cost, but also sometimes by bringing their own equipment, including weapons. Some departments even request donations in exchange for the positions. The Oakley, Mich., police department asks for $1,200, according to Salon.

“These people drop four or five grand and dress up to look like police,” Donna LaMontaine, president of the Deputy Sheriffs Association of Michigan, told the magazine. “I have a problem with that.”

Still, many reserve officers have been hailed as heroes. A number of them have paid with their lives. Others have taken lives.

In a phone interview with The Post on Tuesday, Brewster said that his client’s age and his financial contributions weren’t relevant to the shooting. He described Bates as nimble and sharp, and said he had completed law enforcement training.

“I think that this video went viral and people drew conclusions that weren’t based on fact, and the DA wasn’t strong enough to say no,” Brewster said.

Brewster said Bates was “very, very distraught” after the shooting.

“I don’t think he’s slept in a couple days,” he said.

Professional police officers are of different minds about the reservists, Doug Wyllie wrote in a 2011 article in PoliceOne.

“I believe the ‘part time’ system of policing is absolutely ridiculous,” an unnamed law enforcement official told PoliceOne.com. “The job has changed since walking down the street and spinning your baton. We now encounter more diverse and complicated situations, where we are expected to wear a multitude of hats, and do it perfectly the first time. We contend with more anti-police groups, 24/7 video taping, and more charging and law suit filings then ever before. As such, to do this job without a full salary and full benefits is insane.”

[Oklahoma deputy who killed unarmed man thought he was firing Taser, authorities say]

Indeed, the job means the dangers of police work usually without the compensation. Some reserve officers patrol the streets on foot or on bicycles. Others ride in police cars. Some provide extra security in schools and shopping malls. Others have full police powers.

In California, reserve training is broken up into three levels that total some 900 hours, the top tier ranking them as peace officers, according to Police magazine. In Dorchester County, S.C., it takes about 240 hours of field training to get access to a service weapon and a patrol car, according to the Summerville Journal Scene. In Tulsa, Bates had reportedly trained for hundreds of hours in homicide investigation and decontamination, police told the Tulsa World.

“If they have that badge on, that means they are sworn in by the sheriff,” Capt. John Smith with the Dorchester County Sheriff’s Office, told the Journal Scene, “and the only difference between them and regular officers is they don’t get paid.”

But there’s another difference: Most cops retire long before they’re 73; many retire in their 50s. Some police departments won’t hire anyone past age 40 for the physically demanding jobs.

[How a cellphone video led to murder charges against a cop in North Charleston, S.C.]

But young and old alike become reservists.

For some, reserve programs have become the entry level to full-time police positions. For others, they are an option for retired officers who want to stay on the streets.

“The reserve program is great for departments to fall back on,” one PoliceOne member, Gordon Corey, said. “Even though most reserves are limited commission, if you have full-commissioned officers who are willing to still volunteer as reserves, that gives departments the opportunity to utilize these officers to fulfill call-ins and vacations from full-time officers. With this option, departments won’t have to worry they will make the wrong decision. With reserves who are just reserves and have full time jobs other than law enforcement jobs only make decisions based on what they learn in the reserve police academy which is far less than what a full time officer is taught in the police academy.”

[Man who filmed S.C. police shooting: Maybe God ‘put me there for some reason’]

Years ago, former Los Angeles County Sheriff Lee Baca created a controversial special reserves program for celebrities and, by 1999, it had been eliminated after one recruit was suspended for brandishing his weapon and then another was indicted for international money laundering.

Big names have joined the ranks elsewhere, sometimes seriously, sometimes just for photo ops. Former NBA superstar Shaquille O’Neal has been a reserve officer in Arizona, California and Florida. In 2013, movie star Steven Seagal became a deputy in New Mexico and “Hulk” actor Lou Ferrigno picked up a badge in Ohio.

“I love that I can give back to my community and anyone that needs help with search and rescue,” Ferrigno said, according to Police magazine. “I enjoy doing search and rescue as a reserve deputy. We had a woman who’d fainted in the mountains and needed assistance. We get to her and when we bring her back to consciousness she looks up at me and says, ‘Are you Lou Ferrigno, the Hulk?’ When I told her I was she got all excited and fainted again.

“I felt so bad. We were here to help her, not to make her faint again. Everything turned out fine, but I always laugh about that story.”

[South Carolina killing of Walter Scott leaves two mothers grieving and praying]

But the job is no joke.

In 2005, reserve constable Nehemiah Pickens from Harris County, Tex., was gunned down while assisting in an arrest. In 2013, reserve officer Robert Libke from Oregon City, Ore., was shot and killed when he confronted an armed man who had set fire to his own house. The Reserve Police Officers Association lists more than 200 who have died in the line of duty over the years.

But the nature of the job — usually a volunteer position that varies greatly from department to department in the minimum training required — can pose a danger to the public as well.

“I think reserves, being at work less, have that much more of an obligation to be up on their tactics, officer safety, the law, and policy,” Evan Wagner, a reserve deputy assigned to Los Angeles County’s Lakewood Sheriff Station, told Police magazine. “I think we’re often expected to be weaker in those areas and it makes a big impression when we’re competent. I make mistakes, but try not to twice. We may wear the same badge and uniform and face the same risks, but I don’t think that means we’re entitled to the trust of partners, whose lives will at times depend upon us. I think reserves have to earn regulars’ trust by visibly aspiring to keep themselves at their level of proficiency as much as possible.”

[Cop once hailed as a hero now accused of tickling a dead man’s toes]

During a traffic stop in 2012, Steven Williams, a reserve deputy for the Anderson County Sheriff’s Department, chased a suspect as he fled on foot and, during a struggle over his service weapon, shot and killed Randall Kyle Wilcox. In 2013, a then-62-year-old electrical inspector — also a reserve deputy with the local sheriff’s department — shot himself through the hip while at city hall.

So why accept the risk?

“For me, it isn’t about the money anyway. It isn’t about making arrests either,” James Watson, who has been a reserve deputy for the Dorchester County Sheriff’s Office for more than 20 years, told the Journal Scene. “For me, it’s just helping people.”

“But the way I see it,” he added, “law enforcement, fire service, EMS — it’s not for the pay. It’s more of a calling.”

Correction: The original version of this story, published on April 13, referred to the investigation as a police operation. It was a sheriff’s investigation. It has also been updated multiple times.