The sister of a black pastor who was shot dead by a white police officer despite being unarmed and having his hands up has appealed for justice, saying he did "absolutely nothing wrong".

Terence Crutcher, 40, was first tasered and then shot dead in Tulsa, Oklahoma after police arrived at the scene of his broken down SUV vehicle at around 8pm on Friday.

Officer Betty Shelby shot Crutcher, who was making his way slowly to his car with his hands up. The victim was rushed to hospital but died from his injuries.

Police had claimed that Crutcher was reaching inside his car without his hands up. But footage released by Tulsa Police Department clearly shows the pastor with his hands in the air and his back to the officers.

In footage taken from a police helicopter, an officer can be heard saying: "He's got his hands up there for her now...This guy is still walking and following commands."

But Crutcher was then tasered and shot.

A criminal investigation into the shooting has been opened by the police department, and the federal Justice Department has opened a separate civil rights investigation.

Officer Shelby has given a statement to homicide detectives and been placed on paid administrative leave, according to a police spokesman.

Crutcher's twin sister Tiffany told a press conference of how an officer could be heard in the footage calling her brother a "big, bad, dude".

She said: "I lost my brother, my twin brother who was doing nothing wrong. Absolutely nothing wrong and I truly believe in accountability...We just want answers, we want to know what happened, there's a lot of speculation, but there is one thing, one fact that I do know is that my brother was unarmed. I'm just devastated."

She said her brother had left a class at Tulsa Community College before his SUV stalled on East 36th Street North.

The Crutcher family's legal team, represented by attorney Melvin C Hall, said: "This man had not committed a crime. He was not approached because we suspected of having committed a crime. He was having some difficulty with his vehicle and that's it."

Describing the footage, attorney Damario Solomon-Simmons said: "We saw that Terence was not being belligerent. We did not see Terence reach into the car. We did not see Terence attacking the officers."

Crutcher's family has appealed for any protests over his death to be held peacefully.

The family were shown the footage on Sunday ahead of its public release yesterday.

Tulsa police chief Chuck Jones sought to assure the community that justice would be served and there would be accountability over the incident.

Before releasing the video, he said: "I'm going to tell you right now, there was no gun on the suspect or in the suspect's vehicle. I want to assure our community and I want to assure all of you and people across the nation watching this: We will achieve justice."

He added that he found the video "very disturbing, very difficult to watch."

"It will come out," Jordan said of the details surrounding the fatal shooting, according to Tulsa World. "I will make this promise to you: We will achieve justice in this case."

Campaigning black pastor Jamal Bryant tweeted: "Enough is enough! #terrancecrutcher was killed with his only crime being black in America".

The Tulsa shooting comes after mass protests over black men being shot by police in Minnesota, Florida and Louisiana.

Local activist group We the People called for the immediate arrest of Officer Shelby. Its leader Marq Lewis issued the demand during a news conference yesterday afternoon outside the Tulsa County Courthouse, two hours after the footage was released.

"Tulsa Police Department, you need to arrest her immediately. We don't need to play any longer. You just need to arrest her," Lewis said.