Do inconclusive forensic decisions disadvantage the innocent?

Two experiments examined the potential for inconclusive forensic decisions to disadvantage the innocent.

Both experiments tested the hypothesis that inconclusive decisions produce more incriminating legal judgments than do clearly exculpatory forensic decisions. Experiment 2 also examined whether this hypothesized effect conformed to a confirmation bias, a communication error, or perceptual accuracy.

In Experiment 1 (N = 492), a forensic expert testified that physical evidence recovered from a crime scene either matched or did not match a suspect's evidence or produced an inconclusive result. In Experiment 2 (N = 1,002), a forensic expert testified that physical evidence recovered from a crime scene either matched or did not match a suspect's evidence, produced an inconclusive result, or was unsuitable for analysis. A fifth condition omitted the forensic evidence and expert testimony.

The inconclusive decision produced less incriminating legal judgments than did the match forensic decision (|d|_average = 0.96), more incriminating legal judgments than did the no-match forensic decision (|d|_average = 0.62), and equivalent legal judgments to the unsuitable decision (|d|_average = 0.12) and to legal judgments made in the absence of forensic evidence (|d|_average = 0.07). These results suggest that participants interpreted the inconclusive decision to be forensically neutral, which is consistent with a communication error.

The findings provide preliminary support for the idea that inconclusive decisions can put the innocent at risk of wrongful conviction by depriving them of a clearly exculpatory forensic decision. (PsycInfo Database Record (c) 2024 APA, all rights reserved).