Supreme Court Rules on Biomechanics (Again)

Biomechanics has typically been greeted with skepticism in some Nevada courts, generating far too many motions and accompanying uncertainty.  The Supreme Court has once more addressed this topic, this time in a criminal matter.

In Mathews v. State, Mathews was watching a two year old boy, C.J., when the boy sustained burns to his hands.[1]  The State argued was it was intentional, Mathews said it was an accident.  Mathews disclosed a biomechanical expert, Lindsay Johnson, Ph.D., to testify and dispute part of the State’s case-in-chief.  The district court excluded the expert, concluding “court concluded that Dr. Johnson was not qualified to testify about burns on a child’s skin, and further, his testimony did not have an adequate factual foundation because nobody could testify to his theory of how C.J.’s injuries occurred.”  On appeal, the State argued the Supreme Court had previously “that Nevada law does not recognize biomechanics as a field of expertise, and regardless, Dr. Johnson was not qualified to testify as an expert regarding burn injuries on a child’s skin.”

The district court erred.  It had first concluded Dr. Johnson was unqualified to testify.  But it made “conclusory findings about Dr. Johnson’s medical qualifications without considering whether Dr. Johnson was qualified to testify about the mechanism of C.J.’s injuries.”

The district court also erred in analyzing whether Dr. Johnson’s testimony would assist the jury.  “The State argued that Dr. Johnson’s testimony was based on assumption and not grounded in the facts of the case. The district court repeatedly stated that Dr. Johnson was making up scenarios that were not supported by the facts of the case.”  However, Mathews argued that “Dr. Johnson’s testimony would assist the trier of fact because his testimony offered an alternate mechanism of C.J.’s injuries, which directly refuted the State’s theory.”  The Supreme Court noted “[t]he ‘assistance requirement’ must be assessed in the context of what the burden of proof is and who bears that burden.”  The State had the burden of proof, but “the district court failed to consider the purpose for which Mathews was offering Dr. Johnson’s testimony, which was to rebut the State’s theory that Mathews intentionally burned C.J.”  The State’s witnesses testified it was effectively impossible for the burns to be accidental, but “Dr. Johnson was prepared to testify that it was not impossible and to explain how the child could have tipped the cup and spilled the scalding water on his hands accidentally.”

The Supreme Court reversed.  “Dr. Johnson’s testimony would assist the trier of fact by demonstrating that an accidental mode of injury was possible.  Notably, Dr. Johnson was not testifying to medical causation; rather, the focus of Dr Johnson’s testimony would have been on the mechanics of C.J.’s injury, which was within his scope of expertise and directly refuted the State’s theory.”

The Court also rejected the State’s position that biomechanics was per se unreliable.  The biomechanic rulings in Hallmark and Rish did not bar such testimony.  Instead, like all experts, they must be supported by adequate foundation.  “[B]iomechanical experts are not precluded from testifying altogether, and weaknesses in a purported expert’s testimony, including that one expert may have lesser qualifications than the opposing party’s expert witness, goes to the weight, not the admissibility, of the evidence.”


[1] 134 Nev. Adv. Op. 63 (2018).