Note: This video is graphic and may be disturbing to some viewers.

CHICAGO -- City officials on Tuesday released police dashcam video showing an officer shooting teenager Laquan McDonald 16 times, continuing to fire well after the youth falls to the ground. The court-ordered release of the video came hours after authorities charged Officer Jason Van Dyke with first-degree murder in the teen's killing.

Cook County State's Attorney Anita Alvarez described the 2014 video footage as "chilling" during a news conference hours before its release.

I have no doubt this video will tear at the hearts of all Chicagoans, Alvarez said.

The video shows McDonald, 17, carrying a small knife and walking away from officers. Van Dyke opens fire from about 10 feet away. McDonald's hand jerks out and his body spins around before he collapses to the ground. Van Dyke keeps shooting for as long as 15 seconds -- even after the teen falls.

The video is dramatically different than the initial police account of the shooting. Chicago police said at the time that McDonald was acting strangely and lunged at police before an officer fired.

Court documents laying out the state's case against Van Dyke say the veteran officer emptied an entire clip of ammunition into the teenager, then attempted to reload:

Officer A reported that there was a brief pause in the shots when he looked at defendant and saw that he was preparing to reload his weapon. Officer A could hear McDonald struggling to breathe, told defendant to hold his fire so Officer A could approach and kick the knife away.

All 16 shell casings from Van Dyke's weapon were recovered at the scene.

McDonald is seen in the video lying on the ground for more than a minute before the video cuts off.