When Can Forensic Psychologists Comment on the Credibility of Criminal Defendants?

Forensic psychological examiners are often confronted with assessments in the guilt phase of criminal cases in which a Defendant denies his/her charged conduct, but the existing evidence clearly contradicts their account. This happens often in cases involving charges of violence, sex offending and or substance abuse ( Langton, Barbaree, Harkins, Arenovich, McNamee & Peacock, 2008). What is the proper role of the examiner in such instances?; granting the benefit of the doubt and accepting the Defendant’s account, using the one contained in the differing evidence, or making an independent judgment about which is more likely to be true? Does accepting any version mean the expert is offering an opinion on the Ultimate Issue in the case, and encroaching on the role of the Trier of Fact? The Federal Rules of Evidence (FREE) dictate that judgments about Ultimate Issues belong solely to the Trier of Fact, yet the DSM-5 Manual (APA, 2013) instructs us to consider Malingering in every forensic situation; i.e. is the Defendant being honest about his mental state, and by implication, his/her credibility