The police are reliant on CCTV and security cameras in there everyday jobs. Whether they are in vehicles, bicycles or on foot. They act as a mobile witness to back them up when there has been an incident they have been involved in and the images may be needed in court to help ascertain what exactly happened.
In the days when there were no or at least very few CCTV cameras in operation it was often the criminals word against the police officers which is not enough. So therefore having sufficient evidence in the way of CCTV is vital in there day to day jobs. They also come in useful when a complaint is made against a police officer whether it is an assault of some sort or a suspect claims of being unfairly treated.
These CCTV cameras can be mounted on vehicle dashboards or can be body worn usually clipping on to the officers jacket or over there ear. If police officers are monitoring town and city centers on a busy saturday night there can be so many people around and so much activity that even witnessing an incident first hand such as a group assault it may be hard to recollect exactly what occurred. So for this reason there body worn surveillance as well as the street CCTV cameras are heavily required when reviewing an incident. They also use this footage to help train officers who do not have experience of situations such as dawn raids or an armed seige.