Article published: 6 October 2026
How often do you see an expert witness themself become part of the reason a criminal conviction is overturned?
That is, in effect, what happened in The King v ZX [2025] NICA 76, a decision of the Court of Appeal in Northern Ireland concerning convictions for murder and attempted murder.
Psychiatric evidence was central to the trial. The defendant’s mental state was directly relevant to the issues the jury had to decide, and both the prosecution and defence relied on psychiatric experts.
What makes the case particularly striking is not simply that the Court of Appeal disagreed with an expert’s opinion. Courts do that all the time. The problem went much deeper. The court concluded that the prosecution psychiatrist’s evidence had evolved in such a way that it could no longer be regarded as the independent product of an expert uninfluenced by the demands of the litigation.
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