Where a defendant is charged with possession of a firearm by a street gang member, a witness must establish that the organization is a street gang either by testifying to a pattern of criminal activity or by being established as an expert on street gangs.The 1st District Appellate Court reversed and remanded a decision from Cook County Associate Judge James B. Linn.On the evening of Aug. 7, 2015, three Chicago police officers from the gang investigation unit were engaged in surveillance, responding to a tip about an armed …