State v. Cox

Testimony of an expert witness regarding the credibility of another witness should not be submitted to the jury when there is a substantial risk of the testimony prejudicing the jury toward a third witness.

Defendant appeals from a conviction of various sexually-related crimes. An expert witness is called to diagnose one of two children giving testimony as being sexually abused. The testimony could not be admitted as a diagnosis, and was instead admitted as witness credibility testimony. Defendant argues that admitting the testimony to the jury was plain error because the testimony of the expert went to the credibility of both children, and prejudiced the jury in determining if either of the children were telling the truth about being abused. The Court held that, without physical evidence of abuse, the expert’s testimony as to witness credibility goes not only as to the child diagnosed, but also extended to the other child who testified. By admitting the diagnosis, the trial court committed plain error by creating a substantial risk of prejudice by the jury. Reversed and remanded.