By Brandon L. Garrett, Richard E. Gutierrez, and Nicholas Scurich in Jurimetrics.
Firearms examiners, who seek to link fired ammunition to a particular gun, have testified in criminal trials for over a century. Research suggests that such evidence is highly persuasive to jurors. However, no studies have examined the effect of divergent conclusions offered by defense firearms examiners, nor have any explored the impact of testimony by research scientists—sometimes called “methods experts”—regarding the scientific foundation and limitations of the firearm examination discipline. The effect these types of testimony might have on jurors is, therefore, unknown. This article in Jurimetrics reports the results of a novel empirical study testing the effects of such defense experts. While most participants found the unrebutted testimony of a firearms examiner sufficient to convict the defendant, guilty verdicts were significantly reduced when the defense called an expert. Further, defense experts reduced the perceived likelihood that the defendant discharged the firearm, the strength of the prosecution’s case, the case-specific reliability of the firearm examination, and the general reliability of the firearm examination. However, critical differences existed between our various conditions involving defense expert testimony.