If a confession is obtained, the investigation is commonly completed, followed by the trial and oftentimes the conviction of the suspect. A confession is considered the queen of evidence. But what happens when an innocent person confesses to a crime that she or he did not commit? This happens more often than one would think. But shouldn’t we then find proof of innocence? When looking at proven cases of innocent convictions, the absence of exculpatory evidence is striking. How can this be?
Let us consider the case of a woman who was raped and killed in Pennsylvania in August 1987. The police investigation focused on Barry Laughman who confessed to the murder after the police misinformed him that they had found his fingerprints at the crime scene. The blood testing showed that the perpetrator as well as the victim had type A blood. However, Laughman had type B blood. This information should have excluded him as the perpetrator. At trial, however, an alleged expert who knew about the confession introduced speculative, unfounded theories that “explained” the change in blood type. And so Laughman was convicted to life in prison.
This case demonstrates how a confession can influence the evaluation of other evidence. Such information not only has the potential to affect fingerprint evaluations, but also blood tests and even DNA analyses, as research has shown. How is that possible? Contrary to general believes, the evaluation of physical evidence comprises subjective components. Fingerprints found at the crime scene are often incomplete and DNA samples of poor quality. If this is the case, room for interpretation unfolds and the available context information (e.g., a confession) can exert its influence on the evaluation of evidence, for example when an expert is to decide whether two fingerprints are sufficiently similar. It is in these ambiguous situations that primarily cues supporting the prior hypothesis are considered (forensic confirmation bias).
Laughman was exonerated based on DNA analyses after 16 years in prison. The results of this analysis were believed, despite the confession.
Keywords: False confessions, miscarriage of justice, forensic confirmation bias
Kassin, S. M., Bogart, D. & Kerner, J. (2012). Confessions that corrupt evidence from theDNA exoneration case files. Psychological Science, 23, 41-45. doi:10.1177/0956797611422918
Kassin, S. M., Dror, I. E. & Kukucka, J. (2013). The forensic confirmation bias: Problems,perspectives, and proposed solutions. Journal of Applied Research in Memory and Cognition, 2, 42-52. doi:10.1016/j.jarmac.2013.01.001
Written by Teresa Schneider and Melanie Sauerland, this blog was originally published in German at de.in-mind.org.