An offender seeking to rely on mental impairment as reducing moral culpability must adduce expert evidence that exposes the reasoning process behind the causal opinion, states the expert's qualifications and experience, identifies the factual basis, and explains the extent of the contribution of the impairment to the offending. Tentative or unexplained expert opinions will not discharge the onus on the offender to establish a causal connection on the balance of probabilities. A sentencing judge who raises concerns about expert evidence during the hearing satisfies procedural fairness obligations without being required to adjourn of the judge's own motion.
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