NMSC: Evidence of Susceptibility to a Mental Condition Not Admissible to Negate Intent

In State v. Yepez, the New Mexico Supreme Court examined whether a defendant accused of murder could introduce expert testimony that a genetic condition made him incapable of forming the intent to kill. For reasons related to the specifics of the testimony, the Court concluded that the district court had properly excluded it. More generally, the Court held that evidence of “mere genetic susceptibility to a given mental condition is not relevant on the issue of deliberate intent.”

Background

The defendant killed his adoptive mother’s boyfriend during an argument, after which he set fire to the body. At his trial for murder, he sought to introduce evidence that he was genetically predisposed to violent behavior and therefore could not have had deliberate intent to kill (intent is an element of murder that the State is required to prove). The court excluded the evidence and a jury convicted him.

On appeal, the court of appeals affirmed. In doing so, however, it concluded that the decision to exclude the expert evidence was error. However, it was able to affirm anyway since it also concluded that the error was harmless. A court will not reverse a jury verdict based on an error that ultimately made no difference in the outcome.

Analysis

Whether to admit expert testimony is an evidentiary issue, subject to review for abuse of discretion. This is a difficult standard that most often results in affirmance. To win on appeal, the defendant was required to show that the decision to exclude the expert was clearly against the logic and effects of the facts and circumstances of the case, clearly untenable, or not justified by reason.

To decide whether to admit the evidence, the court was required to look at three factors: (1) whether the expert was qualified; (2) whether the testimony would be of assistance to the trier of fact; and (3) whether the expert’s testimony would be about scientific, technical, or other specialized knowledge with a reliable basis. There was no dispute that the expert was qualified. But the Court concluded that his testimony would not assist the jury.

Whether the testimony would assist the trier of fact itself involved two inquiries: whether it was reliable, and whether it “fit” the facts of the case. The Court found that it did neither. This part of the analysis involved a detailed look at the actual testimony. While interesting, it is case-specific and probably not terribly helpful for future cases.

Reliability

What is more interesting is the Court’s discussion of the court of appeals opinion. In concluding that the testimony should have been admitted, the court of appeals had relied on a case called Acosta v. Shell Western Exploration & Production. In Acosta, the district court excluded expert testimony because it believed there was too large a gap between “association” and “causation”. In doing so, the court had followed United States Supreme Court precedent. The New Mexico Supreme Court reversed, explaining that in New Mexico this was a question reserved for the jury. Here, even when the science is undeveloped or inconclusive, a jury can decide the issue so long as the court believes that the methodology the expert used in reaching an otherwise scientifically inadequate conclusion was sound.

Here, the court of appeals read Acosta to mean the district court could not exclude the expert on the basis that the gap was too large. But the supreme court explained that that was not what had happened. Unlike Acosta, where at least the jury could look at the expert’s methodology, here there was no evidence of the steps the researchers took between the evidence and their conclusions. Acosta therefore did not apply, and it was not error to exclude the expert opinions.

Fit Between Evidence and Expert Opinion

The Court did not end its analysis there. In the second part of its reasoning (relating to the “fit” between the evidence and the expert testimony), it examined whether the expert testimony tended to show that the defendant was incapable of forming specific intent to kill. The Court agreed that the expert testimony showed that a no-activity MAOA genotype, if present, would tend to negate the element of deliberate intent. But the record did not show that the defendant had the rare no-activity MAOA genotype. The experts had extrapolated the no-activity genotype findings to the defendant’s low activity-genotype, a leap which the Court described as speculative.

The Court also noted that the testimony suggested that the low-activity genotype might make persons susceptible to a mental condition that negated deliberate intent. But the question was not whether the defendant was susceptible–it was whether he actually had a condition that negated intent at the time he killed the victim. The court therefore held that evidence of “mere genetic susceptibility to a given mental condition is not relevant on the issue of deliberate intent.”

Having affirmed the district court’s decision and explained the error in the court of appeals opinion, the Court rejected the defendant’s request for a new trial and affirmed his conviction for second-degree murder.

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