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Defendant’s MAOA Gene Evidence Deemed Inadmissible in Murder Case

Citation: State v. Yepez, 428 P.3d 301 (N.M. Ct. App. 2018)

Summary: In July 2018, 31-year-old defendant Anthony Blas Yepez was convicted of second-degree murder, tampering with evidence, and unlawful taking of a motor vehicle after beating a 75 year old man to death in Santa Fe, New Mexico. However, while a neuropsychological evaluation uncovered that Yepez had a genetic, neurological condition — a low-activity MAOA gene —  that Yepez’s experts testified is “statistically associated with the occurrence of maladaptive, or violent, behavior in individuals who have experienced maltreatment in childhood,” this expert testimony was deemed inadmissible in trial court. The state argued that “the evidence was not reliable, not relevant, and so complicated it would confuse and mislead the jury.” Additionally, the state maintained that “current literature does not establish a ‘direct link’ between a low-activity MAOA variant and increased violent behavior.”

Yepez appealed his case to the New Mexico Court of Appeals, arguing that this expert opinion testimony was essential to the trial, as it showed that Yepez was unable to form deliberate intent. Yepez argued that because of the omission of this expert testimony, his conviction should be reversed and he should be granted a new trial. However, the New Mexico Court of Appeals concluded that while the trial court should have included the expert opinion testimony, the exclusion of the evidence did not materially harm Yepez, as the prosecution does not have to prove intent (or premeditation) for a second-degree murder charge. Therefore, the court upheld his conviction.

Key Words: neuroscience admissibility in court, brain science, expert opinion testimony, second-degree murder, New Mexico