Chicago's police superintendent has said videos of the police shooting of a black man in the city last month indicate three officers may have violated the department's policies.
Eddie Johnson said on Saturday that it was against departmental policy to fire at or into a moving car when the vehicle was the only potential use of force by a suspect, and police were taking a hard look at training and tactics following the shooting.
Johnson said the lack of a body-camera video of the shooting of 18-year-old Paul O'Neal is under investigation, though he noted that the officers in that police district had the cameras for only about a week before the shooting.
Reverend Jesse Jackson, the US civil rights activist, said the lack of a complete video accounting of O'Neal's shooting showed a cover-up.
No firearms found
A lawyer for O'Neal's family called for a special prosecutor to investigate the killing.
The union representing Chicago police officers urged the public not to rush to judgment.
Authorities on Friday released videos that captured the moments before and after police shot O'Neal, 18, on July 28.
No firearms were found on O'Neal, who was shot in the back, according to police.
In the video several officers are seen pursuing O'Neal through a back garden and over a fence in a residential neighbourhood while several shots ring out.
Officers are then seen handcuffing O'Neal, who is face down on the ground with blood on the back of his white shirt.
One police officer is overheard in the video cursing the wounded teenager, and telling him "to put your hands behind your back".
No one is seen immediately administering first aid to the teenager. A minute after putting the suspect in handcuffs, the officers mention calling an ambulance.
It was not clear in the video if the teenager was armed, but one officer is heard saying "f**k you shoot at us".
One of the officers is also overheard in the video asking another officer, "They [sic] shot at us too, right?"
'Shocking and disturbing'
The fatal shot is not shown in the video and police are investigating why the body camera of the officer who fired the bullet was not turned on, or if it malfunctioned.
"Please bear in mind that this video material, as shocking and disturbing as it is, is not the only evidence to be gathered and analysed," said Sharon Fairley, an investigator of the incident.
Michael Oppenheimer, a lawyer for O'Neal's family, described the shooting as "one of the most horrific things" he had seen, in a news conference.
He accused the police of carrying out the "execution" of a "loving son".
The video from July 28 was made public by the agency that investigates Chicago police misconduct.
It was the first time the city has made video of a fatal police shooting public after adoption of a new policy that calls for the police to do so within 60 days.
The new transparency is an attempt to restore public confidence in the police department after video released last year showed Laquan McDonald, a black teenager, being shot 16 times by a white officer.
The killing spurred protests and led to the dismissal of the former police superintendent.
Al Jazeera's Alan Fisher, reporting from Washington DC, said the swift release of the video demonstrated that the Chicago police department is adopting a new approach to address allegations of racial bias.
"By taking this prompt action, the police is hoping obviously to show that they are doing things different now, and hoping that that will keep protesters off the streets," he said.