A gunman who fatally shot a Chicago police officer’s son and wounded his friend last summer mistook them for rival gang members, police officials said Friday in announcing a break in the investigation.

Arshell “Trey” Dennis III, who was about to start his junior year studying journalism at St. John’s University in New York City, had returned to his Southwest Side home for a few days last August to visit his parents at their Wrightwood neighborhood residence.

Source