This is my submission to the Ministry of Justice Call for Evidence on computer evidence in criminal proceedings.
Some takeaways from 24 pages of rather dense legal analysis:
- The evidential presumption of reliability (properly so called) is a different animal from informal assumptions about the reliability of computers. They are related, and the latter may influence attitudes to e.g. the threshold for disclosure applications, or to the basic understanding of what the prosecution has to do to prove a case ‘beyond reasonable doubt’ (as opposed to theoretical or fanciful doubt). But the evidential presumption is legally distinct and has a specific, limited, function. The review should cast its net wider than the evidential presumption properly so-called, but equally not confuse it with informal assumptions.
- There is evidently a perception (possibly fostered by the Law Commission 1995 and 1997 recommendations) that the presumption of reliability applies automatically to all computing devices. I don’t think the caselaw supports that. As I read the cases, the court can decide whether or not to apply the presumption.
- If the prosecution deploys expert evidence on reliability the presumption is irrelevant: it’s a matter of deciding between experts. So for general purpose computers and software (i.e. excluding breathalysers, speed guns etc, where the presumption is routinely relied upon) how often does the prosecution actually rely on (and then the court apply) the presumption? This is a question for criminal practitioners (which I am not). I have found no reported criminal cases (other than where accuracy was not questioned), but will readily stand to be corrected if there are any.
- Reliability of computer evidence always has to be considered in the context of what specifically is sought to be proved by it (which can vary widely). For instance, to make a general point, adducing computer records to evidence presence of a transaction is different from proving absence. The latter requires the computer records to be not just accurate, but complete.
- It should not be forgotten that a defendant may wish to adduce computer evidence (e.g. a video taken by them on their mobile phone).
- There may be a distinction to be made between the output of general purpose computing systems and dedicated forensic tools.
- It may also be pertinent to consider whether the computer evidence sought to be relied upon is central to the prosecution’s case, and whether it is corroborated or uncorroborated.
- A computer evidence regime that is predicated on whether a document is ‘produced by a computer’ is potentially problematic, for two reasons. First, there is hardly a document now that has not been touched by a computer at some point in its history. Are those all ‘produced by a computer’? Second (as presaged in the caselaw on S.69 PACE 1984), a bright line definition of that kind is liable to give rise to satellite disputes about what does and does not fall on either side of the line. It may be more fruitful to view matters through the lens of a regime for documentary evidence generally.
- The proposed distinction between generated and captured or recorded evidence is difficult to apply conceptually. The practical examples given in the Call for Evidence throw up many questions.
- Any proposed computer evidence regime should be tested against concrete hypotheticals. I have suggested a list of fourteen, drawn from reported cases.
[Updated 16 April 2025 with a list of takeaways]
