A police spokeswoman said she did not know what Terence Crutcher was doing that prompted police to shoot
Footage has emerged of an unarmed black man who was killed by a white police officer walking away from officers towards his vehicle with his hands up.
Video shows Terence Crutcher walking to his SUV and a female officer following him in Tulsa, Oklahoma.
The 40-year-old is then shocked with a stun gun and fatally shot.
Tulsa Police Chief Chuck Jordan said Mr Crutcher had no weapon on him or in his vehicle.
It is not clear from the footage what led Betty Shelby, the officer who fired the fatal shot, to draw her gun or what orders officers might have given Mr Crutcher.
Local and federal investigators are examining Friday's shooting to decide whether there should be criminal charges or if Mr Crutcher's rights were violated.
In the footage Mr Crutcher's vehicle is stopped in the middle of the road.
As he approaches it, three male officers walk up and Mr Crutcher appears to lower his hands and put them on the vehicle.
The officers then surround him, making it harder to see his actions from the dashboard camera. Another video showed helicopter footage of the incident.
Mr Crutcher is seen falling to the ground, and someone on the police radio says: "I think he may have just been Tasered."
One of the officers near Mr Crutcher moves away slightly.
Almost immediately, a female voice can be heard saying: "Shots fired."
Crutcher's head then drops.
A voice can be heard on the police radio saying, "Shots fired. We have one suspect down."
Police initially said Mr Crutcher was not obeying officers' commands, but police spokeswoman Jeanne MacKenzie said on Monday she did not know Mr Crutcher was doing that prompted police to shoot.
Two 911 calls described an SUV that had been abandoned in the middle of the road.
One unidentified caller said the driver was acting strangely, adding, "I think he's smoking something."
Mr Crutcher's twin sister, Tiffany Crutcher, called for charges to be filed.
"The big bad dude was my twin brother. That big bad dude was a father," she said.
"That big bad dude was a son. 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."