responsibility of the police is to fight crime, maintain order, and provide miscellaneous services to the public. Patrol remains the basic manner in which police services are delivered to the public.
Criminal investigation is the most glamorous aspect of policing. Most police officers regard detective work as “real” police work. Detective work has a specific mission: apprehending the offender. The quality of work can also be measured in terms of the number of arrests. This contrasts sharply with patrol duty, which largely involves peace-keeping. Good detectives are believed to be able to solve most crimes, so the citizen-victim becomes angry when the police fail to solve the crime he or she suffered from.
The process of investigating a crime involves several different steps performed by at least three different units within the police department: patrol officers, detectives, criminalistics technicians. the two major stages of the investigation process are the preliminary investigation and the follow-up investigation.