State v. Yepez, 483 P.3d 576

Background

Defendant Anthony Blas Yepez killed George Ortiz and was charged with first-degree murder (plus related counts); jury convicted him of second-degree murder, tampering with evidence, and unlawful taking of a vehicle.
Yepez sought to admit expert testimony that he has a low-activity MAOA genotype combined with childhood maltreatment, producing a genetic predisposition to impulsive violence offered to negate deliberate (specific) intent required for first-degree murder.
The State moved to exclude the testimony as unreliable, insufficiently probative of impulsive violence in individuals, and likely to mislead the jury; it also noted gaps in corroboration of Yepez’s abuse history and in the genetic testing evidence.
At a Daubert/Alberico hearing the district court found the underlying MAOA+maltreatment research generally met Daubert factors but excluded the experts’ specific opinion that Yepez was predisposed to impulsive violence because (1) experts failed to show reliable methodology tying the studies to impulsive violence, (2) no testing expert (Lightfoot) testified to definitively classify Yepez as having a no-activity MAOA genotype, and (3) the studies predict general antisocial outcomes, not impulsive violence in an individual.
The Court of Appeals reversed, finding the district court impermissibly excluded testimony for an "analytical gap" that should be left to the jury; the New Mexico Supreme Court granted certiorari and reversed the Court of Appeals, holding the district court did not abuse its discretion and affirming the conviction.

Issues

Issue	Plaintiff's Argument (State)	Defendant's Argument (Yepez)	Held
Admissibility of expert testimony that low-MAOA + maltreatment shows predisposition to impulsive violence (to negate deliberate intent)	Testimony was unreliable, risked juror confusion/determinism, and lab author (Lightfoot) did not testify	Scientific literature (Caspi et al., meta-analyses) supports admissibility; testimony relevant to specific intent	No abuse of discretion: excluded because experts failed to show reliable methodology linking low-MAOA to impulsive violence in this individual and lacked necessary fit/applicability
Whether the underlying MAOA+maltreatment research satisfies Daubert/Alberico reliability factors	Underlying science is not sufficiently precise to predict individual impulsive violence	Research is replicated and peer-reviewed; supports probative value	Court: underlying research on increased risk of antisocial behavior meets Daubert factors, but that does not validate the specific expert conclusions offered here
Whether Acosta/Joiner principles prevent exclusion based on an "analytical gap"	Court of Appeals misread Acosta; exclusion was justified	Court of Appeals relied on Acosta to say analytical-gap determinations are for jury	Acosta does not permit admission absent a disclosed, reliable methodology; here experts did not explain methodological steps from group research to individual impulsivity, so exclusion proper
Prejudice / need for new trial (constitutional claim)	Exclusion was not prejudicial; harmless error if any	Exclusion deprived Yepez of a defense to deliberate intent and affected lesser-included determinations	Held: No fundamental or constitutional error; exclusion not prejudicial and conviction affirmed

Key Cases Cited

Daubert v. Merrell Dow Pharm., 509 U.S. 579 (U.S. 1993) (standard for admissibility of expert scientific testimony)
General Elec. Co. v. Joiner, 522 U.S. 136 (U.S. 1997) (analytical-gap concept in exclusion analysis)
State v. Alberico, 861 P.2d 192 (N.M. 1993) (New Mexico rule requiring reliability of scientific methods for expert testimony)
Acosta v. Shell W. Expl. & Prod., 370 P.3d 761 (N.M. 2016) (admissibility of expert opinion where methodology adequately explained; jury weighs strength)
State v. Balderama, 88 P.3d 845 (N.M. 2004) (expert evidence that tends to negate deliberation is admissible when properly founded)
State v. Downey, 195 P.3d 1244 (N.M. 2008) (abuse-of-discretion standard for expert admission and requirement of fit/reliability)
State v. Torres, 976 P.2d 20 (N.M. 1999) (use of Daubert factors in New Mexico)
State v. Boyett, 185 P.3d 355 (N.M. 2008) (expert testimony required to show incapacity to form specific intent)