How Police Investigate Crime

A criminal investigation in England and Wales typically begins when a crime is reported or discovered by police. The investigation process is governed by the College of Policing's Authorised Professional Practice (APP) on investigation, PACE 1984, the Criminal Procedure and Investigations Act 1996 (CPIA), and the relevant PACE Codes of Practice.

The initial response involves securing the scene, ensuring the safety of any victims, and gathering initial accounts from witnesses. This period, known as the "golden hour", is critical for evidence preservation. Officers will secure the scene, identify and separate witnesses, initiate house-to-house enquiries if appropriate, and arrange for forensic examination. A crime scene manager may be deployed for serious offences. CCTV, dashcam footage, and digital evidence sources will be identified early.

Once the initial evidence is gathered, the investigation moves into the development phase. This involves pursuing lines of enquiry to identify suspects, corroborate or contradict accounts, and build the evidential case. Investigators will review CCTV, analyse phone records, conduct forensic examinations, interview witnesses under section 9 of the Criminal Justice Act 1967 (for written statements), and interview suspects under caution. The investigation must be conducted in accordance with CPIA duties: the investigator must pursue all reasonable lines of enquiry, including those that point away from the suspect.

When the investigator believes there is sufficient evidence, the case is referred to the Crown Prosecution Service (CPS) for a charging decision (for indictable and either-way offences). The CPS applies the Full Code Test: there must be a realistic prospect of conviction (the evidential stage) and it must be in the public interest to prosecute (the public interest stage). For summary offences, the police may charge without CPS authority. The case file, including evidence, unused material schedules, and any defence statement, is then prepared for court.