Who is Robert Tennard? His neighbors thought they knew him. They were sadly mistaken. When the two men invited Tennard and his two friends into their home, they fell prey to a savage attack. One host succumbed to a hatchet wielded by one of Tennard's companions. Tennard, however, preferred a knife, which he used to stab the other murder victim fifteen times before making off with the decedents' property.
Convicted of capital murder, Tennard at his punishment hearing introduced evidence intended to show mental retardation. This included a recorded IQ of 67, and testimony regarding an extraneous rape offense to the effect that Tennard had naively believed his victim was using the bathroom "to take a bath" when in fact she was escaping through a window.
Sentenced to die, Tennard unsuccessfully appealed his conviction. He then filed a post-conviction application for writ of habeas corpus, arguing that the jury applied specialized issues in a way that prevented consideration of the mitigating evidence of mental retardation, as required by the U.S. Supreme Court in Penry v. Lynaugh, 492 U.S. 302(1989).
Holding: The Court denied relief, ruling that Tennard was not entitled to a Penry instruction. For Penry to apply, the applicant for relief must prove not only mental retardation, but that his mental retardation rendered him unable to appreciate the wrongfulness of his conduct when he committed the offense.
The Court found no evidence that Tennard was mentally retarded, relying on the three-part test outlined by the American Association on Mental Retardation (AAMR): (1) sub-average general intellectual functioning, (2) concurrent deficits in adaptive behavior, and (3) onset during the early development period. While Tennard produced evidence of a low IQ, this in itself did not meet the standard.
Even if Tennard's low IQ constituted mental retardation, he would still not be entitled to relief, due to his failure to prove that his sub par intelligence rendered him unable to comprehend moral culpability.
Dr. Yates comments: Most striking about Tennard is that despite the defense strategy, no mental health expert was retained to corroborate or refute the available data and to evaluate each component of the court's definition of mental retardation. No evidence could therefore be offered for or against appreciation of wrongfulness of conduct, the ability to learn from mistakes, ability to control impulses, or the ability to evaluate consequences of his actions because no current assessment was conducted to address any of these issues. Let's look at how this would have best been done.
Whenever the question posed to the forensic expert involves cognitive capacity, multiple measures of intelligence should be administered to reduce any possible negative biases of any one measure as well as to assess varying aspects of intelligence. Furthermore, measures should be selected which maximize the possibility of accurately estimating the individual's true potential, tests that take into account the background of the defendant. For example, if the defendant was born, raised, and educated in a different country—whether or not English was the primary language—tests which rely heavily on an American education or which are culturally bound would not be ideal as they would likely considerably underestimate the defendants intelligence.
The Wechsler Adult Intelligence Scale—Revised (WAIS-R) is the most widely used measure of intellectual functioning. Nevertheless, a truncated version eliminating those subtests most influenced by formal education may be more appropriate for a defendant who dropped out of school early in the academic process. Again, a battery of appropriately selected intelligence tasks would yield the best understanding of premorbid capacity.
HOW TO EVALUATE FOR MENTAL RETARDATION: Multiple measures of intelligence
- Tests that consider the examinee's background
- Assess the examinee's executive functioning
- History of neurological injury
- Collateral functioning
Intellectual functioning is best estimated by a score range rather than by a single test score. Confidence levels are utilized to maximize the possibility that achieved scores reflect an accurate estimate of one's intellectual potential. Calculation of a confidence level involves the addition and subtraction of a fixed value to an obtained score yielding a range of lower and upper limit. For example, if the WAIS-R, had been used to obtain a Full Scale IQ of 67 and Mr. Tennard was 23 years of age, his IQ would be reported as FSIQ = 67 + 3; lower limit 64, upper limit 70.
Secondly, it is essential to assess the defendant's executive functioning. Executive functioning includes abilities such as identifying and successfully completing goals; planning, anticipating, and modifying behavior based on external feedback. Executive functioning represents the quality of how one lives one's life. As with intelligence testing, multiple tasks that assess overlapping as well as unique processes should be administered to reduce the chance of misinterpretation or error. These abilities are also relevant to the probability of future dangerousness. Someone with intellectual deficiencies who is unable to learn from experience, to act without anticipating the impact or consequences of his actions, and/or to inhibit behaviors is much more likely to be at risk for potentially injurious behavior than someone who possesses those skills.
Finally, results from the intellectual and neuropsychological test, history, and collateral information need to be evaluated in the context of the specific elements of the crime. Was the crime spontaneous or planned? If planned, how detailed a plan? How organized, and with what time frame? Are the findings from the evaluation consistent with or a departure from the essential features of the instant offense? One may score within the mentally retarded range and even meet criteria for mental retardation as defined by the American Association on Mental Retardation (MMR) and still be responsible for the crime for which he is accused.
