A white former Oklahoma reserve deputy who fatally shot an unarmed black man when he mistook his firearm for a stun gun has been released from prison after serving less than half of his four-year sentence.

Department of Corrections spokesman Matt Elliott says 76-year-old Robert Bates was freed on Thursday morning from the North Fork Correctional Center in western Oklahoma.

Bates was found guilty of second-degree manslaughter in the April 2015 fatal shooting of 44-year-old Eric Harris during a traffic stop.

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Early release: Former Oklahoma reserve deputy Robert Bates, 76 (pictured left in April 2015), was released from prison Thursday, after serving less than half of his four-year sentence for the shooting death of Eric Harris, 44 (right)

Bates, a former insurance executive, was convicted in May 2016 (pictured) of second-degree manslaughter

The former Tulsa County sheriff's volunteer deputy was released after serving just over 16 months behind bars because he got credit for good behavior. Bates will be on probation for nine more months.

The Harris shooting drew thousands of county residents to petition for a grand jury to investigate allegations that Bates, a millionaire retired insurance executive, was unqualified to serve as a deputy but was kept on the force because of his close ties to indicted ex-Sheriff Stanley Glanz.

Attorneys for Harris' family put out a statement saying that the ex-deputy is being released early, 'in time to celebrate Thanksgiving and Christmas with his family,' even as his victim's loved ones continue to mourn his death.

'Now that Mr. Bates is out of prison, it is our expectation that the civil rights suit filed against him and Former Sheriff Glanz will finally begin to intensify,' the statement concluded, according to NewsOn6.

On April 2, 2015, Bates, then aged 73, was taking part in an undercover gun sale sting operation when he confronted Harris.

Harris was shot during a gun sale sting operation in Tulsa, which was caught on camera

Video of the encounter showed Bates chasing the unarmed black suspect (pictured)

In an attempt to subdue him, Bates went to grab his Taser, but later claimed he was unaware he had actually pulled out his gun instead (pictured on the ground)

Final moments: The fatally-wounded Harris can be heard saying: 'Oh my god, he shot me! He shot me!'

Video of the encounter showed Bates chasing the unarmed suspect.

In an attempt to subdue him, Bates went to grab his Taser, but later claimed he was unaware he had actually pulled out his gun instead.

In the video, which was released by the sheriff's office, Bates can be heard shouting 'Taser! Taser!' When the gun goes off, he says: 'I shot him! I'm sorry.'

The fatally-wounded man can be heard saying: 'Oh my god, he shot me! He shot me! He shot me, man' before adding: 'Oh, my god. I'm losing my breath!'

Bates resigned his position in the sheriff's department in the days following the shooting.

He was found guilty of manslaughter in May 2016 and began serving his four-year sentence the following month.

Bates, pictured above on May 31, 2016, was trained to be a Tulsa Police Department patrolman in 1964 but left in 1965

At 6.45am on Thursday, Bates walked out of the North Fork Correctional Center in Sayre a free man, having accumulated time for good behavior and other credits.

Bates, who sold his insurance business for $6million in 1999, was trained to be a Tulsa Police Department patrolman in 1964 but left in 1965.

He was out of law enforcement for 35 years, returning for volunteer work in Florida in 2000 before joining the Tulsa County force in 2008 and making a number of donations to the agency.