A US police department in Oklahoma has released video of an encounter in which an unarmed black man was shot dead by a white officer while his hands were up.

Video recorded by a police helicopter and a patrol car's dashboard camera were released by the Tulsa police department on Monday show 40-year-old Terence Crutcher being shocked with a stun gun and then shot dead.

In the incident, which happened at about 7:40pm on Friday, Betty Shelby, a Tulsa police officer since 2011, shoots once and kills Crutcher while responding to a stalled vehicle report, according to the police department.

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A man in the police helicopter circling above the scene is heard saying during the incident: "Time for a Taser," and "That looks like a bad dude, too. Probably on something."

When a second police car arrived as back-up, Crutcher had his hands up as he walked away from Shelby, who was following him with her gun pointed at his back. She was soon joined by three more officers, according to the dashboard video of the second squad car.

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Crutcher was shot less than 30 seconds after the second car arrived, US media reported.

Before the release of the incident's video and audio recordings, Police Chief Chuck Jordan announced that Crutcher had no weapon on him or in his four-wheel drive vehicle.

The initial moments of Crutcher's encounter with police are not shown in the footage.

Dashboard cam off

Shelby did not activate her patrol car's dashboard cam, said Tulsa police spokeswoman Jeanne MacKenzie. Only the second patrol car's dashboard cam was on.

Local and federal investigations are under way to determine whether criminal charges are warranted.

It is not clear from the footage what led Shelby to draw her gun or what orders officers might have given Crutcher.

Officer Shelby said Crutcher repeatedly ignored her commands. Her lawyer, Scott Wood, was quoted by the Tulsa World newspaper as saying there is more to the story than the videos show.

He said the confrontation had been under way for almost two minutes before the videos began to record.

Shelby believed Crutcher behaved like a person under the influence of the narcotic PCP, Wood said. 

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Tulsa police offical Dave Walker told the Tulsa World that investigators recovered a vial of PCP in Crutcher's SUV. But attorney Damario Solomon-Simmons said even if drugs were present, Shelby still had no justification for shooting the man because Crutcher did not pose a threat.

After the shooting, Crutcher could be seen lying on the side of the road, a pool of blood around his body, for nearly two minutes before anyone checked on him.

When asked why police did not provide immediate assistance once Crutcher was down, MacKenzie said, "I do not know that we have protocol on how to render aid to people."

Brady Henderson, legal director of the American Civil Liberties Union of Oklahoma, said each of the officers present were complicit in the "unconscionable, reprehensible, and disgusting killing" by allowing him to bleed to death on the street without summoning immediate medical aid.       

"The Tulsa officers have made it abundantly clear how little regard they have for Tulsa's communities of colour," Henderson said.

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"By shooting a defenceless black man and then shirking their legal and moral obligation to render aid ...  [the officers] clearly could not care less about whether the black citizens they are sworn to protect live or die."

Crutcher's twin sister, Tiffany Crutcher, called for criminal charges.

"The big bad dude was my twin brother. That big bad dude was a father. That big bad dude was a son," she said.

"That big bad dude was enrolled at Tulsa Community College, just wanting to make us proud. That big bad dude loved God. That big bad dude was at church singing with all of his flaws, every week. That big bad dude, that's who he was."

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Source: Agencies