Do Inconclusive Forensic Decisions Disadvantage the Innocent?

Objective: Two experiments examined the potential for inconclusive forensic decisions to disadvantage the innocent. Hypotheses: 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. Method: 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. Results: 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. Conclusion: 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.