Can expert testimony on suicide risk assessment be admitted without foundation for post-mortem application? State v. Lopez Explained

In State v. Lopez, the Utah Supreme Court addressed critical issues regarding the admission of expert testimony and prior bad act evidence in a murder case where the central question was whether the victim died by suicide or homicide.

Background and Facts
Komasquin Lopez was charged with murdering his wife Shannon after she was shot in the head while they were driving home from his workplace. Lopez claimed Shannon shot herself during an argument, while the State argued Lopez killed her. The physical evidence was inconclusive—the medical examiner could not definitively determine the manner of death, gunshot residue was found on Lopez’s hands but only showed he was in proximity when the gun discharged, and blood spatter analysis was inconclusive. Both Shannon and Lopez had methamphetamine in their systems at the time.

Key Legal Issues
The case presented two main evidentiary challenges. First, whether expert testimony using the Fluid Vulnerability Theory of Suicide (FVTS) was admissible under Utah Rule of Evidence 702 to assess whether Shannon was likely to commit suicide. Second, whether evidence of Lopez’s prior acts of pointing guns at family members was admissible under Rule 404(b) to prove identity rather than impermissible character evidence.

Court’s Analysis and Holding
The Utah Supreme Court found both evidentiary rulings were erroneous. Regarding the expert testimony, the court held that while FVTS may be generally accepted for assessing living patients, the State failed to establish adequate foundation that the theory could reliably assess suicide risk in deceased individuals. The expert had never interviewed Shannon and relied solely on materials selected by the State. For the Rule 404(b) evidence, the court found the prior acts lacked sufficient similarity to establish a modus operandi and did not support any intermediate inference of identity, making them impermissible propensity evidence.

Practice Implications
This decision emphasizes that practitioners must carefully distinguish between the general acceptance of a scientific theory and its specific application to novel circumstances. The court’s analysis also reinforces that Rule 404(b) evidence must serve a genuine non-character purpose and cannot simply show a defendant’s propensity to commit similar acts. Both errors were deemed harmful given the inconclusive nature of the remaining evidence, leading to reversal of the conviction.