Cognitive bias is a widely researched and accepted occurrence in the science of psychology. Anyone is susceptible, including police officers, forensic scientists, witnesses, lawyers, juries and judges. Cognitive bias has been found to be a common thread in wrongful conviction cases.
Cognitive bias is a mental shortcut that simplifies decision-making. We have developed mental shortcuts for many beneficial reasons including saving time and processing a lot of information quickly. Unfortunately, shortcuts are not helpful when deciding guilt in a criminal case.
Cognitive bias causes someone to focus on information that already supports their beliefs, while ignoring information that goes against it. For example, choosing to only recognize evidence that condemns someone you already believe to be guilty of a crime. It is a natural and subconscious process, making it especially problematic in the judicial system.
For example, cognitive bias likely played a role in the wrongful convictions of two men for murder in Los Angeles. Both men were suspected to be guilty in these separate cases. A series of errors in the investigation were overlooked before going to trial. Investigators committed to their convictions despite evidence against a guilty verdict, ultimately leading to the men serving a combined six decades in prison. The men contacted attorneys for post-conviction relief and were eventually exonerated. Los Angeles agreed to pay them a total of $24 million.
An issue in forensic science
Forensic science errors are often found in wrongful conviction cases due to cognitive bias. Forensic analysts may be biased when examining hair traces, bloodstain patterns and fingerprints in criminal cases. A person’s existing expectations may influence their evidence collection and interpretation. Forensic experts may form beliefs due to learning about facts in the case, such as if they are verifying a match or if someone confessed.
In fact, a study found that confessions affect analysis of handwriting evidence. Participants who were told that the defendant confessed were more likely to say that the handwriting samples were similar and written by the same person.
Forensic analysts and all parties in the justice system must be aware of the influential nature of cognitive bias and work to prevent it.