Neuropsychologists uniquely inform the criteria for cognitive impairment and fitness to stand trial. Referrals frequently involve detailing the relative impact of acquired brain injury, intellectual deficit and mental illness, whilst referencing Section 6 -Victorian Crimes (Mental Impairment and Unfitness to be Tried) Act 1997. Summary expert witness evidence provided for the Director of Public Prosecutions related to charges of distributing child pornography in the form of a ‘scientific treatise’. This 65 year-old divorced and tertiary educated father without prior criminal history had suffered a mid-cerebral artery stroke 10 years prior to offending. He had superior verbal intellect with reduced, albeit functionally normal, visuo-perceptual reasoning. His claim that his ‘most important discovery for mankind’ had compelled him to distribute his 'treatise was formulated as evidence of a crystallising organic-based Delusional Disorder. During the intervening period up to the trial the defendant made a complaint to AHPRA regarding that opinion: there was no case to answer. Neuropsychological opinion mapped the defendant’s gradual functional decline since the stroke and implicated neural degeneration. Contrasting Forensic Psychiatry and Clinical Psychology evidence concluded the defendant was fit to stand trial despite his ‘poor judgement’ and ‘errant beliefs’. The Jury found the defendant unfit to stand trial.