Criminal Law Practitioner
Abstract
Firearms examiners can evaluate associations between suspect ammunition and ammunition test-fired by a suspect firearm by microscopically comparing tool marks on both projectiles. This practice has been criticized, including by the National Academy of Sciences, yet firearms examiners routinely testify as experts in the United States. Jurors must determine the weight of expert evidence, which lawyers can aim to discredit on cross-examination or rehabilitate on redirect-examination. Using online vignettes, the authors investigated how both cross-examination and redirect-examination affected potential U.S. jurors' certainty about expert firearms evidence.
Participants (n=114) were asked to rate their certainty (on a scale of 0-100) about the validity of three expert statements – Very Certain (an exact match), Certain (a match to a reasonable degree of certainty), and Uncertain (evidence is unsuitable for comparison)—when assigned to one of three conditions. These conditions were a judicial instruction about weighing the evidence (control condition); a cross-examination referencing criticism of firearms evidence, and a redirect-examination (following the cross-examination). Referencing the routine admission of firearms evidence.
Analysis was undertaken both between groups and between the statements given to each group. Results suggest that experts conveying high certainty create higher certainty in jurors, cross-examination has a detrimental effect on this certainty, but redirect examination does not reduce this detrimental effect.
Recommended Citation
Shooter, Dr. Amelia; Scanlon, Dr. Paraic; and Cooper, Professor Sarah L.
(2025)
"Juror Certainty about Firearm Evidence: Examination Effects,"
Criminal Law Practitioner: Vol. 15:
Iss.
1, Article 3.
Available at:
https://digitalcommons.wcl.american.edu/clp/vol15/iss1/3