When a crime is reported to the police an investigation takes place. The nature of that investigation will change depending on whether the crime is recorded as a minor or serious offence, but all investigations follow similar lines of enquiry. This process of investigation will include taking statements from the victim and witnesses and assessing the scene. The investigation will also involve checking all available resources including criminal databases and public tips. It is important that police investigate all available lines of enquiry in order to build a strong case and ensure that evidence does not get missed. If a police officer becomes too wedded to a pet theory and ignores lines of enquiry this can cause miscarriages of justice.
Police investigate by examining the physical crime scene, looking for trace evidence like weapons, bloods and fibres. They may take photographs, measurements and objects for examination in a laboratory. They may also send in soil and hair samples to test for the presence of certain substances. Police officers are trained to be able to recognise and collect these kinds of materials. They are incredibly skilled at this and they are vital to solving criminal cases.
Police departments carry out pattern and practice investigations to identify problematic policing in their areas and to remedy them. They may look at issues such as excessive force; discriminatory policing; or failing to address concerns raised by community members. The outcome of a pattern and practice investigation can enable law enforcement agencies to reform their policies, restore community confidence in the police, and foster safe and effective policing.