Disturbing video footage has emerged showing the moment a white police officer shot dead an unarmed black man - who had his hands raised above his head.
Father-of-four Terence Crutcher can be seen slowly walking towards his vehicle which had stalled in the middle of the road in Tulsa, Oklahoma on Friday evening.
Police, responding to reports of an abandoned vehicle, claimed Mr Crutcher was refusing to follow their orders.
Warning: this video contains graphic images that some people may find disturbing.
The 40-year-old was tasered by one officer and then fatally shot by another.
He can then be seen falling to the ground in a bloody heap.
A female officer is heard saying: "Shots fired!"
Before Mr Crutcher was fatally shot, an officer in a police helicopter is heard saying: "That looks like a bad dude."
The killing comes amid a nationwide debate over police's use of force on the African-American community following recent high-profile cases of unarmed black men dying at the hands of officers.
Tulsa Police Chief Chuck Jordon, who called the footage "disturbing", confirmed on Monday that no weapon was found on Mr Crutcher or in his vehicle.
He has ordered the Justice Department to investigate the incident, promising Mr Crutcher's family "we will achieve justice".
The police officer who fired the fatal shot has been placed on paid leave while the case is reviewed.
In a tearful press conference, Mr Crutcher's twin sister said: "That big bad dude - his life mattered."
The family's lawyer accused police of treating Mr Crutcher "like a criminal".
"Instead of giving him a hand, they gave him bullets."
Hillary Clinton, the Democratic presidential candidate, called the shooting "intolerable" and said "systemic racism" must be tackled.
"We've got to tackle systemic racism. This horrible shooting again -how many times do we have to see this in our country?" she told the Steve Harvey radio show.
"An unarmed man with his hands up. This is unbearable and should be intolerable. We've got to do everything to improve policing and go after bias. There are good police officers - we've seen them in New York after terrorist attacks. We've got to have law enforcement and communities respect each other."