The Limited Diagnosticity of Criminal Trials

Abstract

A fundamental function of the criminal trial is to determine the facts correctly in order to distinguish between guilty and innocent defendants, and between strong and weak prosecutions. This Article seeks to answer a simple question: How good is the criminal trial at reaching accurate factual conclusions?

The Article applies a body of experimental psychology to examine the ability of factfinders to assess the evidence and draw correct inferences from it. The psychological research indicates that the mental processes involved in determining facts in criminal trials are more complex and fickle than generally believed. Part I exposes the difficulties in deciphering the human testimony that is frequently encountered in criminal trials, including eyewitness identification, witness memory for the event, confessions, alibis, and witness demeanor. The task is further hindered by two systemic problems with the integrity of the evidence: false corroboration and the paucity of the investigative record. Part II demonstrates that the inference-making process is susceptible to distortion from the context of legal decisionmaking. Intrusive factors include courtroom persuasion, exposure to impermissible information, emotional arousal, racial prejudice, and the decisionmaker’s cognitive process itself.

In sum, the accuracy of the criminal trial falls short of the system’s high epistemic demands and the certitude it exudes. The findings contribute to our understanding of the causes of mistaken verdicts, particularly wrongful convictions. The Article proposes ways to improve the diagnosticity of the process.