Ineffectiveness of the "consistent with" judicial limitation on forensic firearm identification testimony

Judicial limitations on forensic firearm identification testimony aim to prevent overstated conclusions declaring a definitive match (or "identification") between bullets or cartridge cases and a specific firearm. The Maryland Supreme Court has ruled that examiners may state only that markings are "consistent with" those from a particular firearm. Another judicial ruling held that examiners may state only that the defendant's firearm "cannot be excluded" as the source of the fired bullets or cartridge cases. These studies examined whether these limitations reduce juror conviction rates.

We hypothesized that jurors presented with "consistent with" testimony would render fewer guilty verdicts compared with "identification" testimony. We also hypothesized that the "cannot be excluded" phrasing would result in fewer guilty verdicts than the "consistent with" or "identification" phrases.

Participants were 475 individuals (Study 1: N = 147, median age = 36 years, 50% female, 50% male; Study 2: N = 328, median age = 41.5 years, 51% female, 49% male) who served as mock jurors. Participants read a criminal trial synopsis involving firearm examiner testimony; each participant was randomly assigned to one of three conditions that varied the conclusion reached by the firearm examiner: "identification," "consistent with," or "cannot be excluded." Participants then rendered a verdict (guilty, not guilty) and rated the probability that the defendant fired the gun. Study 2 included cross-examination to enhance ecological validity.

In Study 1, 65.3% of jurors convicted in the identification condition, 57.4% in the consistent-with condition, and 39.2% in the cannot-be-excluded condition. Study 2 largely replicated these results, with 47.3%, 47.6%, and 32.7% conviction rates, respectively. The "consistent with" phrase did not reduce the conviction rate compared with "identification" in either study.

"Consistent with" did not significantly reduce guilty verdicts compared with definitive identification testimony, suggesting that it may not effectively convey limitations to jurors. Courts may need more robust interventions to limit the persuasive power of forensic firearm identification testimony. (PsycInfo Database Record (c) 2025 APA, all rights reserved).