"This is not justice," said Reverend Marvin Hunter, the great-uncle of slain teenager Laquan McDonald.
As Chicago police officer Jason Van Dyke awaited his fate, threats against the cop and his kin were still being investigated and city schools were bracing for potential civil unrest.
Jurors deliberated fewer than eight hours before reaching a verdict. Van Dyke now faces up to life in prison.
Jason Van Dyke, a white Chicago police officer who fatally shot black teenager Laquan McDonald 16 times in October 2014, is standing trial accused of murder.
An unlawful Chicago cop shooting would have been ignored had it not been for recordings.
The demonstrators chanted, "Sixteen shots and a cover-up!" and "Rahm, resign!"
A Chicago police officer last month was charged with first-degree murder.
Chicago has been roiled by street protests and political turmoil since the release of the video.
Details of when the video would be released were not available.
Chicago mayor faces questions over his handling of a police shooting investigation.
The film's title, "Chi-Raq", is a nod to the prevalence of violent crime in Chicago and Iraq.
Chicago officer Jason Van Dyke is seen on dash cam video shooting McDonald, a black teenager.
Jason Van Dyke allegedly shot the teenager 16 times last year.
McDonald's killing and the 13-month delay releasing any video taken by dashboard cameras on squad cars at the scene have led to days of demonstrations.
Protests were mostly small and peaceful in the days following the release of video footage showing the fatal shooting of Laquan McDonald.
Chicago Police Officer Jason Van Dyke faces first-degree murder charges in the shooting death of Laquan McDonald.
Officer Jason Van Dyke faces 20 years to life if convicted of first-degree murder.
Officials declined on Friday to say exactly when they would make the video public.