Police in Tulsa, Oklahoma, have released a video showing an officer fatally shooting an unarmed black man who had his hands in the air.
The US Justice Department said it was looking into the incident as a possible civil rights violation.
Officer Betty Shelby shot Terence Crutcher, 40, whose sport utility vehicle broke down on Friday, police said.
Mr Crutcher was pronounced dead at hospital.
The case is the latest in a string of shootings of unarmed black men by US police that have raised questions of racial bias in police forces.
"We will achieve justice in this case," Tulsa Police Chief Chuck Jordan told a news conference adding the release of video was done as a matter of transparency.
In one video shot from a police helicopter, Mr Crutcher is seen with his hands in the air, followed by an officer with a drawn weapon. He then puts his hands on the vehicle.
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The victim's sister, Tiffany Crutcher, called for peaceful protests.
"Just know that our voices will be heard, 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 our family" Ms Crutcher said at a news conference.
One of the officers, in audio from the helicopter, says Mr Crutcher is not following instruction. Another says "that looks like a bad dude too, could be on something."
Mr Crutcher then drops to the ground and a female officer can be heard on police radio saying: "Shots fired."
The victim is then seen on his back having been shot.
In a police dashcam video, one officer with a weapon drawn trails Mr Crutcher as he walks to the vehicle. A pop is heard and he falls a few seconds later.
"We think he may have just been Tasered," a man's voice is heard on a police radio. "Shots fired," a woman's voice then says.
One officer, identified as Tyler Turnbough, used his Taser on Mr Crutcher, Tulsa police said, adding Officer Shelby, fired her gun at the man.
She has been placed on administrative leave pending the outcome of the investigation.
The US Department of Justice has launched a separate civil rights inquiry into the officers' use of force, US Attorney Danny Williams with the Northern District of Oklahoma said yesterday.
