In Dubio pro Reo. Behavioral explanations of pro-defendant bias

The standard model of optimal deterrence predicts that the probability of wrongful conviction of the innocent is, at the margin, as detrimental to deterrence as the probability of wrongful acquittal of guilty individuals. We extend the model in several directions: using expected utility as well as nonexpected utility to consider the role of risk aversion, nonlinear probability weighting, and loss aversion. We also consider how relevant emotions such as guilt, shame, and indignation play out. Several of these factors support the intuition that wrongful convictions of the innocent do have a larger detrimental impact on deterrence and thus the policy implications are reconciled with the widely shared maxim in dubio pro reo. We then draw some theoretical implications such as a novel justification for the different standards of proof in criminal vs. civil law as well as other policy implications.