Media playback is unsupported on your device Media caption Dashcam footage shows shooting of Terence Crutcher in Tulsa

The family of an unarmed black man shot dead by police in Oklahoma have called for peaceful protests.

Authorities are investigating the death of Terence Crutcher, 40, who had his hands in the air when he was shot next to his car, relatives say.

Police footage shows Mr Crutcher walking away from officers, his hands in the air, before he is shot.

An officer is heard on a recording from a police helicopter calling him "a big dude" who was "probably on something".

"The big bad dude was my twin brother," his twin sister, Tiffany, told reporters.

"That big bad dude was a father. That big bad dude was a son. That big bad dude was enrolled at Tulsa Community College, just wanting to make us proud.

Image copyright AP Image caption Terence Crutcher's sister Tiffany (centre) and father Joey (right) have spoken out after his killing

"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.''

She went on to ask that people turn out to demonstrate.

"Just know that our voices will be heard," she said. "The video will speak for itself. Let's protest.

"Let's do what we have to do, but let's just make sure that we do it peacefully, to respect the culture of (the Crutcher family)."

In another video filmed inside a police car, Mr Crutcher is seen walking away from officers and toward his vehicle with his hands up before he approaches the door on the driver's side.

Image copyright KTUL/AP Image caption Video shows that Mr Crutcher had his hands up when he was approached by police

There he drops to the ground after a stun gun, and then a gun, are fired.

He died later in hospital, police said.

The video and the helicopter footage appear to back up his family's assertion that his hands were in the air at all times.

Officers came across Mr Crutcher's stalled vehicle while they were en route to another call, reports say.

Image copyright AP Image caption Mr Crutcher was shot while next to his car on Friday evening

A lawyer for Betty Shelby, the police officer who shot Mr Crutcher, said he had ignored officers' commands.

Attorney Scott Wood told the Tulsa World newspaper that Mr Crutcher had repeatedly reached into his pockets, despite being told not to.

Shots were fired when he reached into the window of a vehicle, he said, but it is unclear in the videos what occurred just before the shooting.

The US Justice Department is investigating the circumstances of the shooting.

A series of high-profile incidents involving African-Americans dying at the hands of police have led to demonstrations across the US.