The police investigate a range of incidents such as reported burglaries, violent assaults and road traffic collisions. A key element of the investigation is gathering and analysing evidence to identify suspects and bring them to justice. Investigators must follow appropriate procedures to ensure that evidence does not become contaminated or otherwise invalid. For example, they must photograph crime scenes and record the relative location of objects and bodies. They may also send physical samples (such as blood, fibres and fingerprints) to specialist labs for analysis.
The volume and nature of the material available to investigators varies depending on the crime type. For instance, property crimes generate quite different types and volumes of evidence from shoplifting or burglaries. Investigation officers also have to take into account local cultural and social sensitivities when investigating sensitive cases. In addition to this, all investigators need a good understanding of the legal framework within which they operate. This includes the Police and Criminal Evidence Act 1984 (PACE) and the European Convention on Human Rights.
For example, if an investigator attends a call about a suspected assault with a weapon and finds a suspect inside a house with a bloody knife, the investigation will be classified as a Level One priority. This means that the investigator must protect and collect the evidence in as short a time as possible to prevent further violence. This will involve deploying force where necessary and, in some cases, entering the house under the authority of exigent circumstances.