VIDEO: Anita Alvarez describes dash cam video of Laquan McDonald shooting

CHICAGO -- A Chicago police officer now faces first-degree murder charges in the shooting death of Laquan McDonald, 17. He is being held without bail.

Chicago Police Officer Jason Van Dyke shot the black teenager 16 times in October 2014. The shooting was recorded on a police dash cam video, which will be released by Wednesday.

Cook County State's Attorney Anita Alvarez described the video after Van Dyke appeared in court.

"At 9:57:36, McDonald has crossed over the white lane divider away from the officers, and Officer Van Dyke has taken at least one step towards McDonald with his weapon drawn," Alvarez said. "The officer then opened fire on Laquan, whose arm jerks, his body spins around and he falls to the ground. While Laquan is falling to the ground the defendant takes at least one more step towards him, at which point the angle of the dash camera changes and we can no longer see the officer in the frame of the video. Two seconds later, Laquan McDonald is lying on the street on his right side, and the video captures what appears to be two puffs of smoke coming from the ground near his body. These puffs of smoke were later identified as clouds of debris caused by the fired bullets. At 9:57:51, McDonald is still lying on the street and the last visible shot is fired."

Van Dyke acted "without legal justification and with the intent to kill or do great bodily harm, Jason D. Van Dyke personally discharged a firearm that proximately cause the death of LaQuan McDonald," according to court documents filed Tuesday.