By Mark Weinraub

CHICAGO (Reuters) - Video released on Friday showing the moments before the killing of an unarmed 18-year-old black man by Chicago police last week left anger and unanswered questions as it failed to capture the fatal gunshots because an officer's body camera was not recording.

In the footage released by Chicago's Independent Police Review Authority, two officers can be seen shooting at a stolen car driven by Paul O'Neal, who crashed into a police car then fled into a backyard where he was gunned down.

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, who was shot in the back. It was not immediately clear why there was no footage of the gunfire that killed him.

A lawyer for O'Neal's family, Michael Oppenheimer, told a news conference that the young man had been killed in cold blood and called for a special prosecutor to be appointed in the case.

"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."

Three Chicago police officers have been stripped of their law enforcement authority, a more severe step than a mere suspension, for their roles in the July 28 shooting.

The swift actions appeared aimed at showing Chicago Police Superintendent Eddie Johnson's determination to address swiftly a possibly unjustified use of deadly force.

It was the latest in a string of high-profile killings of unarmed black men by police that have raised tensions between minority communities and law enforcement as well as renewed a national debate about racial discrimination in the U.S. criminal justice system.

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 are all turned off.

In a statement, Johnson said the shooting "raised a lot of questions about whether departmental policies were followed," and he said officers will be held accountable for their actions "should wrongdoing be discovered."

A police spokesman could not immediately be reached for further comment.

The use of force by police against African-Americans in cities from Ferguson, Missouri, to Baltimore and New York has sparked sometimes violent protests, as well as giving birth to a new civil rights movement dubbed Black Lives Matter.

Some people took to social media to question why some of the officers could be seen giving each other high-fives in the video and why some of their cameras were switched off.

Last year, Chicago was rocked by protests after video showed police killing 17-year-old Laquan McDonald, who was shot 16 times in October 2014.

Last year, the Chicago Police Department revised its deadly force policy to bar officers from shooting at moving vehicles if no other weapons were being used against police.

(Additional reporting by Tom Polansek, Writing by Daniel Wallis; Editing by Leslie Adler and Jonathan Oatis)