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Chicago • A white Chicago police officer who shot a black teenager 16 times last year was charged with first-degree murder Tuesday, a day before the deadline for the city to release a video of the killing that many people fear could spark unrest.

City officials and community leaders have been bracing for the release of the dash-cam video, fearing the kind of unrest that occurred in cities such as Baltimore and Ferguson, Mo,, after young black men were slain by police or died in police custody.

Moments before the footage was made public, the mayor and the police chief appealed for calm.

"People have a right to be angry. People have a right to protest. People have a right to free speech. But they do not have a right to ... criminal acts," Police Superintendent Garry McCarthy said.

The judge who ordered the recording's release said it must be put out by Wednesday. City officials spent months arguing that the footage could not be made public until the conclusion of several investigations.

Cook County State's Attorney Anita Alvarez defended the 13 months it took to charge officer Jason Van Dyke. She said cases involving police officers present "highly complex" legal issues and she would rather take the time to get it right than "rush to judgment."

Alvarez said the impending release prompted her to move up the announcement of the murder charge out of concern the footage could spark violence.

"It is graphic. It is violent. It is chilling," she said. "To watch a 17-year-old young man die in such a violent manner is deeply disturbing. I have absolutely no doubt that this video will tear at the hearts of all Chicagoans."

But she insisted that she made a decision "weeks ago" to charge Van Dyke and the video's ordered release did not influence that.

Some community leaders said there was no doubt that Alvarez only brought charges because of the order to release the video from Oct. 20, 2014, that shows the shooting of 17-year-old Laquan McDonald.

"This is a panicky reaction to an institutional crisis within the criminal-justice system," said the Rev. Jesse Jackson, who said he hoped to see "massive" but peaceful demonstrations.

Months after McDonald's death, the city agreed to a $5 million settlement with his family, even before relatives filed a lawsuit.

The city's hurried attempts to defuse tensions also included a community meeting, official statements of outrage at the officer's conduct and an abrupt announcement Monday night that another officer who has been the subject of protests for months might now be fired.

After the judge's order to release it, the investigation was quickly wrapped up and a charge announced.

"You had this tape for a year, and you are only talking to us now because you need our help keeping things calm," the Rev. Corey Brooks said of Monday night's community gathering with Mayor Rahm Emanuel.

Several people who have seen the video say it shows the teenager armed with a small knife walking away from several officers. They say Van Dyke opened fire from about 15 feet and kept shooting after the teen fell to the ground. An autopsy report says McDonald was shot at least twice in his back. It also said PCP, a hallucinogenic drug, was found in his system.

At the time of his death, police were responding to complaints about someone breaking into cars and stealing radios.

Van Dyke, who was denied bond on Tuesday, was the only officer of the several who were on the scene to open fire. Alvarez said the officer emptied his 9 mm pistol of all 16 rounds and that he was on the scene for just 30 seconds before he started shooting. She said he opened fire just six seconds after getting out of his vehicle and kept firing even though McDonald dropped to the ground after the initial shots.

Assistant State's Attorney Bill Delaney said at the hearing Tuesday the shooting lasted 14 or 15 seconds and that McDonald was on the ground for 13 of those seconds.

Van Dyke's attorney, Dan Herbert, maintains his client feared for his life and acted lawfully and that the video does not tell the whole story. Van Dyke, though stripped of his police powers, has been assigned to desk duty since the shooting.

Herbert said the case needs to be tried in a courtroom and "can't be tried in the streets, can't be tried on social media and can't be tried on Facebook."