Deputies wanted evidence on camera.
But when they recorded a sting against an alleged illegal weapons dealer in Tulsa, Oklahoma, earlier this month, cameras also rolled as Eric Courtney Harris ran, and when he was fatally shot.
The Tulsa County Sheriff's Office released the video on Friday. The shooting was an apparent accident, it has said.
The reserve deputy thought he had his Taser in hand, not his firearm, and shot Harris "inadvertently," according to the sheriff's office.
In the last minutes of the video, Harris, a convicted felon, lies on the pavement with police on top of him. An officer calls for a Taser. But in place of an electric clicking sound, a gunshot rings out.
Then a voice can be heard saying, "Oh! I shot him! I'm sorry!" Another officer screams out, "He shot him! He shot him!"
Harris, who is bleeding, calls out, too. He's losing his breath, he says. An officer yells back at him. "You f---ing ran! Shut the f--- up!" he yells. "F--- your breath."
The group of officers begin tugging Harris' hands behind his back as the video ends.
Harris later died at a local hospital. Police said at the time of the shooting that Harris admitted to medics at the scene that he may have been under the influence of Phencyclidine, a street drug commonly known as PCP.
The video is edited to block out the officers' faces. Harris is clearly visible.
'German Luger' deal
Minutes earlier, Harris had climbed into a truck cab, where an undercover officer had set up a camera on the dash to record the suspect.
"What's up?" they greet each other cordially. Without missing a beat, Harris rummages deep in a backpack and hastily hands over a semiautomatic pistol. Every few seconds, he looks around outside nervously.
"Sweet, that's a nice gun, man," the undercover officer says off camera. It's a "German Luger," Harris tells him.
He cranes his head around quickly and watches as a car pulls up next to the truck. Officers in uniform jump out, and Harris bolts out the passenger door and sprints off.
"He's running; he's running, he's running!" the officer in the truck says.
Another video from an officer's body camera picks up the chase. The officer wearing it jumps out of a vehicle and pursues Harris on foot, catching up to him easily. He tackles the fleeing suspect.
The officer commands him, "I need you to roll on your stomach. Now!" Other officers appear. Someone calls, "Taser! Taser!"
The gunshot discharges.
Much later in the recording made by the first camera inside the truck, two men are conversing. "He thought it was his Taser," one of them says, as the other curses in frustration.
In the background, a woman is crying "No, no, no!" Harris had come to the sting deal with a female companion.
Police have said that Harris had reached for his waistband, and officers feared he might endanger them. When Harris was on the ground, he "refused to pull his left arm from underneath his body where his hand was near his waistband," they said after the shooting in early April.
The officer's body camera video did not reveal that area of Harris' body.
The reserve deputy who fired "inadvertently" was placed on administrative leave after the shooting, the sheriff's office has said. Robert (Bob) Bates is 73 years old and a former Tulsa police officer.
When asked by CNN affiliate KTUL whether Bates' age may have been a factor in the shooting, Shannon Clark of the Tulsa County Sheriff's Office said, "Did an accident happen? Sure. But is it accredited to his age? Or was it accredited to the rapidly evolving situation? I guess that will be determined in the investigation."
Asked if another gun was found on Harris, Clark said, "The suspect was placed in the ambulance and transported so quickly. I have not been told there was a second weapon found on him yet."
An officer can be seen in the video taking his foot off of an object lying on the pavement not far from Harris.