Stockley, 36, shot Smith, 24, five times December 20, 2011 after a auto chase that followed a suspected drug deal.
"Orders to disperse were given numerous times".
Following the violence, U2 cancelled their concert scheduled for Saturday night in St Louis, citing safety concerns for fans.
Friday's disturbances began in the afternoon as protesters took to the streets after the court verdict.
If he had been convicted on the charges, the 36-year-old former policeman could have faced life in prison without parole.
Wall Street mixed after record highs
In the bond market, treasuries showed a lack of direction before closing almost flat for the second straight session. The Federal Reserve said the weather and flooding was responsible for nearly all of the loss.
Purdue 35, Missouri 3: Key moments, players and grades
The Boilermakers took advantage of that turnover when Blough connected with Richie Worship for a 1-yard touchdown pass. On the season, Blough is completing over 75-percent of his passes for around 10 yards per attempt.
Stockley said to his partner, in an audio-recorded statement, "we're killing this motherfucker, don't you know", minutes before killing Smith. The gun found in Smith's vehicle later appeared to only have Stockley's DNA. The officer, Jason Stockley, had maintained he shot at Anthony Lamar Smith five times because he thought Smith was reaching for a gun, but prosecutors argued Stockley planted the gun in Smith's Buick after it crashed.
However, Wilson ruled that based on "nearly thirty years on the bench ... an urban heroin dealer not in possession of a firearm would be an anomaly", concluding that Smith had been the owner of the firearm, and referencing the drug found in Smith's vehicle.
During the pursuit, Stockley could be heard saying on an internal police auto video he was going to kill Smith, prosecutors said. He left the force in 2013 and has since moved to Houston, Texas.
The Metropolitan Police Department reports that at least 13 protesters have been arrested and four police officers injured, although police said the protests were mostly non-violent. Judge Timothy Wilson, the circuit judge hearing the trial, acquitted Stockley because he said he wasn't convinced by the prosecution that Stockley "did not act in self-defense". An FBI expert testified that one shot was sacked at Smith from less than six inches away, KMOV reports.