Surveying practicing firearm examiners

Telling us less than what they know: Expert inconclusive reports conceal exculpatory evidence in forensic cartridge-case comparisons.

“…We see two possibilities, both of which might be involved. First, as noted earlier in this article, some labs prohibit their examiners from rendering elimination reports and insist that these examiners render inconclusive reports when perceiving a nonmatch (Dorfman & Valliant, 2022; Scurich et al, 2022). Examiners from those labs might believe that this rule applies to all of their shell-casing tests, whether they are a part of an experiment or are actual cases.…”

Forensic comparison of fired cartridge cases: Feature-extraction methods for feature-based calculation of likelihood ratios

“…Current widespread practice is to report the conclusion as a categorical decision, i.e., as “identification”, “inconclusive”, or “elimination” (or as “unsuitable for analysis”). Existing validation studies of practitioner performance have tended to use a small number of test trials, and have seldom reflected real casework conditions (Smith et al [ 6 ]; Mattijssen et al [ 7 ], [ 8 ]; Scurich et al [ 9 ]).…”

“…In a survey of practitioners presented in Scurich et al [ 9 ], ∼7% of respondents reported that a typical fired-cartridge-case comparison took less than 30 min, ∼24% that it took 30–60 min, ∼28% that it took 1–2 h, ∼26% that it took 2–4 h, and ∼15% that it took more than 4 h.…”

“…In a survey of practitioners presented in Scurich et al [ 9 ], some respondents had skeptical (or even hostile) attitudes toward the use of statistical models for comparison of bullets and comparison of fired cartridge cases, but others had more positive attitudes. One of the respondents with a more positive attitude emphasized the need for developers of statistical models to have a thorough understanding of firearms examination, and another emphasized the need for improved performance and for larger databases.…”

Implicit Blackstone ratios in decisions made by firearm and toolmark examiners.

“…Firearm examiners claim to be extremely averse to false positive errors (Scurich et al, 2022). For example, firearm examiners at the Federal Bureau of Investigation proclaim that “minimization of false positives [is] paramount” to their technique (Monson et al, 2022, p. 5).…”