Pernicious Inferences: Double Counting and Perception and Evaluation Biases In Criminal Cases

As DNA exonerations have brought attention the conviction of innocent defendants, I have noticed a troubling feature of many of the cases. The jury’s decision, although wrong, seemed reasonable because based on multiple strands of independent evidence, all of which had to be erroneous. As one looks closer, however, the evidence is not independent, but the linkages were generally not noticed and sometimes even hidden. The following scenario is one I encountered in practice but hardly noted its dangers. In a robbery case, an identification may be made from the pictures assembled of those suspected in recent robberies, which are reasonable for a robbery squad to use. The array or mug book contains no single target and no clear fillers. If an identification is made of a person on the basis of appearance matching the witness’s memory of the perpetrator and that person has no iron-clad disqualifier (such as confinement in prison when the crime occurred), he becomes not only a suspect but may become a defendant with two items supporting his prosecution. The identification is the first item of incriminating evidence against the suspect. When viewed without knowledge of the criterion used to select the photos shown to the witness, the identification appears to be corroborated by a second independent incriminating fact - the person selected on the basis of physical appearance has a prior record of like offenses. If that prior record includes a quite similar conviction, it may even be admissible at trial as “other crimes” evidence. Clearly these two pieces of evidence are not independent of each other but connected: the individual’s prior record put him in the photo display. Indeed, each of those in the display shares the same incriminating characteristic. Anyone and everyone who might be selected from such photographs would have this second strike against them. However, witnesses and jurors will often effectively perceive the prior record as unique to that person. This double counting or failure to appreciate the co-dependence of evidence arises in a number of different contexts. It may also be involved when informants, particularly “jail house” informants, provide fabricated incriminating statements that they claim were made by the suspect, and a form of double counting is generally part of the story when false confessions are secured from defendants. A number of processes operate to produce and exacerbate the mis-evaluation of evidence. One is contamination. For example, information about an identified suspect’s prior criminal record can filter back to the eyewitnesses, which will generally increase their level of certainty in their identifications. It goes forward to other investigators and prosecutors, influencing their evaluation of other evidence. Subtle psychological influences both contribute to the generation of these pieces of evidence and enhance their perceived strength with jurors. A number of heuristic devices operate on the actors in the process. Several come together under what is often termed “tunnel vision,” which affects investigators and prosecutors causing them to focus attention on this suspect largely to the exclusion of others and of alternative scenarios besides his or her guilt. These pernicious inferences can even affect defense counsel’s perceptions. Others impede accurate analysis of the evidence by jurors. This paper highlights the importance of being sensitive to the potential co-dependence of the types of evidence that are frequently encountered in criminal cases. The impact of such evidence on investigators, prosecutors, and jurors is highlighted and the critical need to ensure independence of proof and proper evaluation is developed.