CHICAGO — A white Chicago police officer who shot a black teenager 16 times last year was charged with first-degree murder Tuesday, hours before the city released 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 turmoil that occurred in cities such as Baltimore and Ferguson, Mo.

A judge ordered that the recording be made public by today. Moments before it was released, 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 relevant portion of the video runs for less than 40 seconds and has no audio.

Laquan McDonald, 17, swings into view on a four-lane street where police vehicles are stopped in the middle of the roadway. As he jogs down an empty lane, he appears to pull up his pants and then slows to a brisk walk, veering away from two officers who are emerging from a vehicle and drawing their guns.

Almost immediately, one of the officers appears to fire from close range. McDonald spins around and crumples to the pavement. The second officer simultaneously lowers his weapon.

The car with the camera continues to roll forward until the officers are out of the frame. Then McDonald can be seen lying on the ground, moving occasionally. At least two small puffs of smoke are seen coming off his body as the officer continues firing. An officer kicks something out of McDonald’s hands.

Police have said the teen had a knife. Cook County State’s Attorney Anita Alvarez said Tuesday that a 3-inch knife with its blade folded into the handle was recovered from the scene.

After the video’s release, protesters began marching through streets. Several hundred people blocked traffic on the near West Side.