CHICAGO — Chicago’s police superintendent on Saturday suggested that an officer’s body camera wasn’t turned on when he fatally shot a black teen last month because the officer had only received it about a week earlier and wasn’t yet proficient in using it.

But demonstrators who held a march protesting the killing voiced suspicions that the camera may have been turned off as part of a coverup.

At a news conference, Superintendent Eddie Johnson discussed nine videos taken from dashcams and body cameras. The videos show officers firing repeatedly at a stolen car as it heads away from them. They also show the officers handcuffing a wounded Paul O’Neal, who was driving the stolen car, after a foot chase through a residential neighborhood in the city’s South Shore section.

‘‘They had had those cameras maybe about a week. . . . There’s going to be a learning curve,’’ Johnson said .

The cameras were introduced to one police district early last year as part of a pilot project. They have since been distributed to six other districts and the officer who shot O’Neal had been issued a camera as part of that rollout, said department spokesman Anthony Guglielmi. He did not know when the remaining 22 districts would be issued body cameras.

Protesters said Saturday that they did not believe any official explanation for the non-working body camera. They and the attorney representing the O’Neal family scoffed when a department spokesman said Friday that the officer’s camera may have been deactivated by the force of the air bag when the stolen car crashed into a police cruiser.

‘‘Since all the other cameras were working, I’m sure that camera was working and it (the shooting) was edited out or that officer turned it off on purpose,’’ said Ja’Mal Green, an activist who spoke at the rally. ‘‘If this is brand new equipment, how come the other officers knew to turn their cameras on and the officer who shot the fatal shot failed to turn his on or it got mysteriously turned off?’’

Release of the O’Neal shooting video was the first under a new policy that calls for such material to be made public within 60 days. The policy was changed after public outrage last year following months of delay in releasing video that showed black teenager Laquan McDonald being shot 16 times by a white officer.

The McDonald shooting video prompted accusations that Mayor Rahm Emanuel had delayed its release until after his reelection and some protesters called for him to resign. Emanuel denied he delayed and he fired Police Superintendent Garry McCarthy, replacing him with Johnson.

‘‘I was concerned by some of the things that I saw on the videos and that’s why we took such a swift action . . . that we did last week to relieve the three officers of their police powers,’’ Johnson said.

Chicago police have not identified the officers involved.

The department’s policy prohibits officers from ‘‘firing at or into a moving vehicle when the vehicle is the only force used against the sworn member or another person.’’ But the policy also says that officers ‘‘will not unreasonably endanger themselves or another person to conform to the restrictions of this directive.’’

The protest Saturday coincided with the 50th anniversary of civil rights leader Martin Luther King’s march in the same neighborhood to protest housing segregation.