Investigation
Investigation — Authorised Professional Practice
Summary
This section of the Authorised Professional Practice (APP) provides guidelines on the investigation process, highlighting the key aspects an investigator should consider when conducting a criminal investigation. It defines a criminal investigation as one aimed at determining whether an individual should be charged or is guilty of an offence. Investigators are advised to follow all reasonable lines of enquiry impartially, gathering evidence that may point both towards and away from a suspect. Victims should be believed for reporting purposes unless clear evidence proves otherwise. The importance of effective case management, disclosure, and supporting victims throughout the process is emphasized to ensure successful outcomes and improve the overall efficacy of the criminal justice system.
Key principles
- 1Follow all reasonable lines of enquiry
- 2Victims should be believed when making complaints
- 3Support victims according to their diverse needs
- 4Accurate recording of investigation outcomes is crucial
- 5Use technical expertise to maximize evidential opportunities
Defined terms
- Code of Practice to the Criminal Procedure and Investigations Act 1996 (CPIA)
- An investigation conducted by police officers with a view to it being ascertained whether a person should be charged with an offence, or whether a person charged with an offence is guilty of it.
Full guidance
This page is from APP, the official source of professional practice for policing.
The Code of Practice to the Criminal Procedure and Investigations Act 1996 (CPIA)(opens an external website in the same tab) defines a criminal investigation as:
> An investigation conducted by police officers with a view to it being ascertained whether a person should be charged with an offence, or whether a person charged with an offence is guilty of it.
Investigators conducting an investigation should impartially follow all reasonable lines of enquiry to gather material which points both towards and away from a suspect. This process may result in the suspect being prosecuted in the courts, an out-of-court disposal or community resolution.
The Home Office (2020) Counting rules for recorded crime(opens an external website in the same tab) states that, when making a complaint, victims should be believed for the purposes of recording a crime, unless it is clear at that point that the incident did not happen.
Investigators should proportionately test material gathered through enquiries, including victim and witness accounts, and use technical and scientific expertise to maximise evidential opportunities. Effective case management and disclosure will support prosecutors and the criminal justice process to achieve successful outcomes.
In many cases an investigation will not find enough material to make a charging decision. This may be because the offender has left very little evidence or there are no viable lines of enquiry to pursue. In these cases it is still important to accurately record the outcome of the investigation for intelligence purposes. This will help the police service to identify crime hot spots and take proactive action to reduce risk and prevent further crimes. In some cases the process of an investigation will also help victims to recover from the impact of crime and access appropriate support services.
Throughout the investigation and criminal justice process, victims should be supported according to their diverse needs, allowing them to give their best evidence. Any risks should be effectively managed and they should be directed to appropriate support services.
Do not provide personal information such as your name or email address in the feedback form. Read our privacy policy for more information on how we use this data
What is the reason for your answer?
APP is the authoritative source for UK policing practice and is updated over time. For the current, official version — including any operational detail not reproduced here — go direct.
Read the full APP guidanceSource: College of Policing — Authorised Professional Practice · Crown copyright, licensed under Open Government Licence v3.0. Summary fetched 2026-06-27.