A video was released of the alleged incident. Investigators said Pierre Robinson shot and killed 23-year-old Glenn Houston, Jr. in 2014 to keep his position in the Evans Mob street gang.
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Also known as "GuttaGang" and "HitzSquad," the faction was described in the indictment as a violent "criminal organization" based on the South Side.
Prosecutors said the shooting happened inside a store in the Chatham neighborhood's 400 block of East 79th Street.
Robinson was found guilty of committing murder in aid of racketeering on Thursday after a four-day trial. His conviction is punishable by a mandatory life sentence, prosecutors said.
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He is due back in court for sentencing in February.
His conviction is punishable by a mandatory life sentence, prosecutors said. Robinson, who has used the alias Javontte Richardson, was previously convicted of gun charges three times in Cook County and sentenced to prison, court records show.
The Sun-Times Media Wire contributed to this report.