When AI meets the witness box: the future of fair trials

Artificial intelligence has finally arrived in the criminal courts, and not in the way anyone expected.

In R v FGD [2026] EWCA Crim 918, the Court of Appeal confronted a genuinely modern problem: what happens when a complainant uses AI to prepare for cross‑examination in a rape trial? The answer, at least in this case, is that the trial Judge wrongly halted the proceedings. However the judgment goes much further, sounding a clear warning for practitioners, police, and policymakers about the risks AI poses to witness evidence.

This case is about the integrity of evidence in an era where AI can produce persuasive, personalised, and dangerously influential content at the click of a button.

The facts

The respondent (R) was on trial for rape. The complainant (C) was the sole Prosecution witness. After a day of cross‑examination regarding where they had been at a particular time on the evening in question, C went home, searched their cloud storage, and produced screenshots showing their movements on the night in question.

That prompted the defence to request a full phone download, which was surprisingly granted by the trial Judge.

From the download, two documents were found containing a detailed summary of C’s recollection of events followed by a series of questions in the form of cross-examination of C’s account together with suggested answers.  It appeared to be a documentary record of witness coaching. Witness coaching is strictly prohibited, as it interferes with the integrity of a witness’s evidence. When C was asked who they had been communicating with, they said they had “put stuff into AI to help me prepare myself for the Court”.

The defence applied to stay the proceedings for abuse, on the limb that a fair trial was impossible, as it was not clear what evidence was C’s, and what evidence was as a result of the AI coaching. The Judge agreed, and stayed the proceedings as an abuse of process.

The Prosecution appealed the ruling.

The appeal

The central issue was simple: did the Judge err in concluding that the AI coaching made a fair trial impossible?

The Court of Appeal held that he did. Three themes stand out.

Stays are a last resort

The Court emphasised the long‑established principle from the caselaw that even serious irregularities can usually be cured by the trial process. There were a number of other options open to the Judge to try and ensure a fair trial could still take place and he had not appeared to consider these. These included:

• Matters concerning the reliability and credibility of C’s evidence could be safely left to the jury, where they had been appraised of the nature and content of the AI documents accompanied by a robust direction from the Judge
• The AI coaching related to C’s cross-examination. They had provided their evidence in chief in the usual way, through a pre-recorded video interview shortly after C first complained to the police. Therefore it was only C’s answers in cross-examination that had to be assessed against the coaching content from AI.

The AI coaching was fully recorded

Unlike traditional witness coaching, which is usually done in secret and without any form of recording, here all the AI “coach” had provided to C was fully recorded and could be placed in its entirety before the jury or summarised by agreement.

As such, this transparency made the situation more manageable, not less.

The Judge relied heavily on a concession that should not have been made

Prosecution Counsel appeared to accept that coaching necessarily made a fair trial impossible. The Court of Appeal disagreed and encouraged future Counsel to explicitly explore all remedial options before inviting a Judge to stay proceedings.

The Court’s warning about AI

The final section of the judgment is striking. Lady Justice May issues a clear, forward‑looking warning:

• Witness coaching is prohibited – whether done by a person or by AI.
• Witnesses must be firmly discouraged from using AI to prepare evidence. Doing so could run the risk of unfairness, with evidence having to be excluded in extreme cases.
• AI use may trigger wider disclosure obligations, particularly with the use of open AI and personal information going into the public domain, which may ultimately result in intrusive phone downloads.
• AI systems may store personal information in ways complainants do not anticipate.
• Police, the CPS, and the Criminal Procedure Rules Committee should urgently consider regulation of AI use in criminal proceedings.

This is the first time the Court of Appeal has directly addressed AI use by witnesses. It is unlikely be the last.

Comment

R v FGD sets the tone for future cases involving witnesses using AI. If a witness uses AI to “prepare”, that interaction may become disclosable, and may justify examination of devices that would otherwise remain untouched.

This is an important reminder that AI can influence memory, shape narrative, create persuasive but artificial “consistency” and contaminate evidence in ways that are difficult to detect.

The Court of Appeal’s approach is pragmatic but clear: AI coaching is serious, but not automatically fatal. The trial process can be robust enough to deal with AI coaching without the trial having to be stayed, provided Judges and advocates engage with the issue properly. Clear jury directions about AI influence may become routine.

This judgment is a wake‑up call. AI is already shaping how witnesses think, remember, and present their evidence. The criminal justice system must now decide how to respond.

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