Chain of custody 1170/2025

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FOI Reference: 1170/2025

Request

I am investigating how AI-assisted evidence analysis is documented and reported within existing Chain of Custody (CoC) and Audit Trail (AT) structures.

For the sake of clarity, I have included a glossary at the end of this document. CoC is used here as an umbrella term encompassing related concepts such as continuity, chain of evidence, and provenance; while AT refers to any documentation system that captures and records the forensic processing of evidence

Is the chain of custody (CoC) and/or audit trail (AT) recorded when digital evidence, broadly speaking, are processed and analysed?

If yes, please provide:

1. Details of the information that is recorded (e.g., evidence identifiers, date/time of transfers, personnel identifiers, storage/access logs, integrity checks)
2. Details of any technical or procedural methods used to record or track the CoC and/or AT. Kindly specify if the process is automated, manual, or hybrid.
3. Please indicate whether any verification or validation procedures are in place to confirm that digital evidence, upon acquisition, is a genuine and unmodified record rather than a synthetically generated or manipulated.
4. Any guidelines, practice directions, or policies guiding the documentation of CoC and/or AT for digital evidence, including any templates or forms. Kindly attach or reference related documents.
5. Has your force conducted any internal evaluations or comparisons regarding the efficiency, accuracy or reliability of automated, manual, or hybrid reporting methods? If yes, please provide copies or references.
6. Is the maintenance of a CoC and/or AT managed in-house or outsourced?
7. If in-house, provide details of the responsible role(s) or department(s), including any training materials or internal guidance relevant to this task.
8. If outsourced, please provide the name of the provider(s), a description of their role, and any related contract document(s).

Clarification received

The focus of my request is on what information is captured and logged in chain of custody (CoC) and audit trails (AT) during the processing of audio and textual evidence, including where AI systems may have been used.

For clarity, “processing” includes activities applied to evidential material such as transcription, translation, redaction, or summarisation.

Evidence types
The request covers audio and textual digital evidence processed for legal or investigative purposes:

- Audio evidence: Recorded sound collected, preserved, and analysed for evidential use. Examples include body-worn camera audio, dashcams, emergency call recordings, and investigative interviews.
- Textual evidence: Written or encoded content collected, preserved, and analysed for evidential use. Examples include interview transcripts, statements, emails, chat logs, social media content, and system-generated transcripts (e.g., speech recognition outputs).

These examples are illustrative rather than exhaustive.

While the research focus is on audio and textual evidence, “digital evidence, broadly speaking” as written in question 4 indicates that information on visual evidence (e.g., CCTV, body-worn video, photographs) may also be included if available. This may provide useful context, particularly regarding chain of custody and audit trail practices.

Lifecycle stage
The primary focus of this research is on the analysis stage. Information on CoC and AT across other stages of the evidence lifecycle is welcome if possible.
Chain of Custody vs Audit Trails
Please provide separate information for CoC and AT.
Time frame
Please provide information held from 1 January 2021 to the date of the request.

Response

Section 1 of the Freedom of Information Act 2000 places two duties on public authorities. Unless exemptions apply, the first duty at Section 1(1) (a) is to confirm or deny whether the information specified in a request is held. The second duty at Section 1(1) (b) is to disclose information that has been confirmed as being held.

Where exemptions are relied upon Section 17 of the Freedom of Information Act 2000 requires Dyfed Powys Police, when refusing to provide such information (because the information is exempt) to provide you the applicant with a notice which: (a) states that fact, (b) specifies the exemption in question and (c) states (if that would not otherwise be apparent) why the exemption applies.

I can confirm that Dyfed-Powys Police does hold the information you have requested. However, we are withholding the whole of the requested information since we consider that the Section 12(1) exemption the Cost of Compliance exceeds the Appropriate Limit applies to it.

Section 12 (1) – The cost of compliance exceeds the Appropriate Limit

Section 12(1) states: “…Section 1 (1) does not oblige a public authority to comply with a request for information if the authority estimates that the cost of complying with the request would exceed the appropriate limit.”

The cost of providing you with the information requested in respect of your request is above the amount to which we are legally required to respond i.e. the cost of locating and retrieving the information exceeds the “appropriate level” as stated in the Freedom of Information (Fees and Appropriate Limit) Regulations 2004. It is estimated that it would exceed 18 hours (i.e. minimum of 21 hours) to comply with this part of your request. The regulations can be located @ https://www.legislation.gov.uk/uksi/2004/3244

The Freedom of Information department has been advised that the information in respect of Question (d) of your request is not held in an easily retrievable format. In light of this and in order to accurately obtain the information relative to your request for the time frame stipulated would involve Dyfed Powys Police accessing and manually reviewing 125 pages of documents.

It has also been established that it would take a minimum of 10 minutes per page to review and obtain the information for a single record in respect of your request.

The process outlined results in the below time estimate:-

A dip sample of 6 work instructions and SOPs along with 10 controlled forms.

MD SOP 03 Prelims - 23 pages - 10 mins per page (230 mins)

DFU SOP 09 Exhibit Handling - 31 pages - 10 mins per page (310 mins)

DFU SOP 11 Direct Submissions - 15 pages - 10 mins per page (150 mins

DFU WI 03 Outsourcing - 16 pages - 10 mins per page (160 mins)

DFI WI 12 Submissions - 9 pages - 10 mins per page (90 mins)

CDE SOP 17 Imaging Lab - 21 pages - 10 mins per page (210 mins)

We have 10 forms that records forms of AT and COC - 10 mins per page (100 mins)

Time estimate to complete task = 21 hours

In accordance therefore with the Freedom of Information Act 2000, this letter acts as a Refusal Notice for the Whole of this request under Section 17(5) A public authority which, in relation to any request for information, is relying on a claim that section 12 or section 14 applies must, within the time for complying with section 1(1), give the applicant a notice stating that fact.

You may wish to refine and resubmit your request so that it reduces the time shown above to fall within the 18 hours, should you require any further advice in relation to this matter please don’t hesitate to contact the Freedom of Information Unit. Please also be advised that should the request be refined, it does not remove the public authorities right to cite exemptions if relevant.

Although excess cost removes the forces obligations under the Freedom of Information Act to provide any further information, as a gesture of goodwill, I have provided information, relative to the remaining questions of your request which has been easily retrievable and outlined below. I trust this is helpful, but it does not affect our legal right to rely on the fees regulations for the remainder of your request.

Response Q1