Reducing Unjust Convictions : Plea Bargaining, Trial, and Evidence Suppression/Disclosure

We develop a dynamic model of the disposition of a criminal case, allowing for the potential discovery of exculpatory evidence by prosecutors (who choose whether to disclose this evidence) and by defendants, as the case proceeds from arrest through plea bargaining and (possibly) trial. We characterize equilibrium behavior by prosecutors and defendants, under three different disclosure regimes: (1) no disclosure is required; (2) disclosure is required before trial; and (3) disclosure is required from the point of arrest onward. A prosecutor who has (resp., has not) privately observed exculpatory evidence is called an “informed” (resp., “uninformed”) prosecutor. When no disclosure is required, an informed prosecutor makes a lower plea offer than one who is uninformed; no case is dropped voluntarily. When disclosure is required only prior to trial, then an informed prosecutor makes the same offer as an uninformed prosecutor, but an informed prosecutor will disclose and drop the case following a rejected plea offer. Finally, when the prosecutor is required to disclose prior to plea bargaining, then an informed prosecutor discloses and drops the case, whereas an uninformed prosecutor makes the same offer as in the no-disclosure regime, and never voluntarily drops the case. In all regimes, some innocent defendants accept the plea offer and others reject it (and similarly for guilty defendants). We find that both regimes requiring some disclosure, as compared with a no-disclosure regime, are (at least weakly) more likely to convict the guilty and less likely to convict the innocent (regardless of whether the prosecutor is informed or uninformed). However, the more-limited disclosure regime, as compared to the more-extensive regime, leads to a higher likelihood of conviction for innocent defendants facing an informed prosecutor, but a lower likelihood of conviction of innocent defendants facing an uninformed prosecutor and a lower likelihood of conviction of guilty defendants