Plea Bargaining and Investigation Effort: Inquisitorial Criminal Procedure as a Three-Player Game

We study the impact of plea bargaining on decision errors and operating costs of the inquisitorial justice system. Scholars and legal professionals are divided over whether such plea deals are compatible with the inquisitorial tradition. In this paper, we stylize inquisitorial criminal procedure as a sequential game with two benevolent investigators, judge and prosecutor. Both agents are subject to private investigation costs and seek a correct decision over a defendant of uncertain guilt. Our analysis shows that the introduction of plea deals in courtroom helps to overcome the problem of effort coordination between the two investigating agents. All equilibria that involve a conviction also adhere to the ‘beyond reasonable doubt’-conviction threshold. Moreover, we demonstrate that plea bargaining reduces the frequency of wrongful convictions (type I errors) in inquisitorial procedures.