Chicago police have released video showing the moments before officers killed an unarmed 18-year-old black man but failed to capture the fatal shots because a policeman's body camera was not recording, prompting allegations of a cover-up.
In the footage released by Chicago's Independent Police Review Authority on Friday, two officers can be seen shooting at a stolen car driven by the man, Paul O'Neal, who crashed the Jaguar into a police car and then fled into a backyard where officers gunned him down.
Chicago Police Superintendent Eddie Johnson said in a statement the July 28 shooting "raised a lot of questions about whether departmental policies were followed", adding officers would be held accountable for their actions "should wrongdoing be discovered".
The clips included police cuffing O'Neal as he lay with his shirt bloodied, while one officer cursed him.
"They shot at us too, right?" one officer can be heard saying, referring to the occupants of the stolen Jaguar.
No firearms were found on O'Neal, whom police shot in the back.
A lawyer for O'Neal's family, Michael Oppenheimer, told a news conference the young man had been killed in cold blood and called for a special prosecutor to be appointed in the case to pursue possible criminal charge against officers.
"What I saw was pretty cold blooded," Oppenheimer said.
"There is no question in my mind that they ran this kid down and murdered him."
In one of the video clips, an officer can be seen gesturing toward other officers' body cameras after the shooting and telling them to make sure they were all turned off.
Chicago-based civil rights leader the Reverend Jesse Jackson told Reuters the lack of footage of O'Neal's killing was "a cover-up".
"The force was excessive. It was unnecessary. It was an execution," Jackson said.
In response to a Reuters query about why there was no video of the shooting of O'Neal, Chicago police spokesman Anthony Guglielmi said, "This is under investigation. The cameras either were not activated or they were impacted by the collision."
He said police in the district had received the body cameras just eight to 10 days before the shooting and "officers have not had a lot of time to interact with the equipment".
"This is something the department is looking into and will be doing a technical analysis of the cameras to help shed some light on what may have happened," Guglielmi said.
Three Chicago police officers have been stripped of their law enforcement authority, a more severe step than a suspension, for their roles in the shooting.
A string of high-profile killings of black men by police in various US cities in the past two years has renewed a national debate about racial discrimination in the American criminal justice system and given rise to the Black Lives Matter movement.
Chicago's Fraternal Order of Police urged people not to rush to judgment in the case.
"Due to the fact that this chaotic incident occurred in a matter of moments, each individual perspective needs to be taken into consideration," the union said in a statement.
Some people took to social media using the hashtag #PaulONeal to question why some of the officers could be seen giving each other high-fives in the video and why some cameras were switched off.
Last year Chicago was rocked by protests after video showed police shooting a 17-year-old named Laquan McDonald 16 times in October 2014. Authorities said McDonald was armed with a knife and had slashed at the tyres and window of a patrol car.