Police investigation is the process of examining all the evidence in a case to determine whether a criminal offence has been committed and who might have committed it. Investigation includes gathering and analysing physical evidence; interviewing witnesses, victims and suspects; and using information obtained from other sources like CCTV and public records.
An investigation may also take in other factors such as policing by consent, a duty to promote good relations and equality law (such as section 11 of the Children Act or section 149 of the Equality Act). The results of investigations can be documented so that the force has a record to show how well it is meeting its legal responsibilities.
When a crime is reported, it will often trigger an immediate police response. This will depend on the nature of the incident and whether the alleged perpetrator is still at the scene. If the alleged perpetrator is still at the crime scene, law enforcement officers will investigate what happened to identify and arrest them for the offence.
For incidents where a suspect is not at the scene, investigators must have reasonable grounds to detain or arrest them. This requires them to have a clear idea of what offence they are investigating and why they are acting, which they should be able to explain when asked by a court.
Once a case has been completed, investigators will prepare a file to present to prosecutors for consideration as to whether to prosecute or negotiate. Having an accurate account of the evidence and the investigation in this form will help to ensure that future cases are more effective. This is called ‘learning from experience’ and can be done in a variety of ways including reviewing past investigations and considering successful strategies and areas for improvement.
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