In later seasons CCTV, GPS and Cell phone tracking might be used to trace suspect(s) and victim(s) movements by the Police. The detectives may even ask victims and witnesses to look through photographs in mug books or to view police lineups where they will try and identify the suspect(s). If gang or drug connections are suspected the detectives might talk to other Police units/squad specializing in those types of crimes. They may even approach Criminal Informants to see if they have heard anything on the street about the crime itself.