CHICAGO - Chicago officials have released a video of a white police officer fatally shooting a black teenager last year.

The move Tuesday follows a judge's order last week to release the squad car dash-cam footage. Seventeen-year-old Laquan McDonald was shot 16 times on Oct. 20, 2014. Police say he refused to drop a knife.

Lawyers who have seen the video say it shows McDonald with a small knife and walking away from officers. They say Officer Jason Van Dyke opened fire from about 15 feet and kept shooting after the teen fell to the ground.

Some worry the images could lead to the kind of unrest seen in Baltimore and Ferguson, Missouri, and other cities after young black men were slain by police or died in police custody. Chicago Mayor Rahm Emanuel and Police Superintendent Garry McCarthy urged calm ahead of the video's release, that it's up to the justice system to hold Officer Jason Van Dyke accountable.

Laquan's family also released a statement calling for calm, saying "No one understands the anger more than us but if you choose to speak out, we urge you to be peaceful." It adds, "Don't resort to violence in Laquan's name."