MENTALLY ILL OFFENDERS VIS-A-VIS THE CHALLENGES OF ADMISSIBILITY OF OPINION EVIDENCE IN NIGERIA

Abstract

The paper critically examines the evidence of mentally ill offenders’ vis-a-vis investigating the challenges of admissibility of opinion evidence in Nigeria. In cases requiring abstruse or technical knowledge which are outside the knowledge and understanding of the court or jury, opinions of those deemed knowledgeable in those faculties are often sought. This is in consonance with the rule that the testimony of experts constitute exception to the generally accepted rule that when a court is to form an opinion on a relevant fact in issue, opinions of other persons are irrelevant and inadmissible. But the judiciary has maintained a skeptical and cautious attitude toward the admissibility of opinion evidence of experts. This stems from the controversial and conflicting testimonies of experts. This paper appraises the admissibility of opinion evidence as it concerns mentally ill offenders. It presents various legal commentaries and judicial decisions on the concept – both expert and non-expert opinion evidence. The paper distinguishes between professional witnesses and expert witnesses. The paper also states that the courts have often favoured traditional methods of assessing culpability of the mentally-ill offender. It concludes however, that the courts have often rejected opinion evidence of experts because of the unreliable and conflicting testimonies of psychiatrists and other experts – regarding such testimonies as probative, advisory, not essential and do not tie the hands of the court.