The dangers of convictions based on a single piece of forensic evidence

Abstract

The overall goal of the criminal justice system is to ensure that perpetrators of crimes are duly punished and that victims of crimes are duly exonerated. As part of the effort to achieve this goal, the forensic disciplines have become very important in criminal investigations and prosecutions in identifying the guilty and in exonerating the innocent. There is a growing number of cases where people have been convicted based on a single piece of forensic evidence. However, some of the convictions have been found to be wrong, largely, due to the lack of adequate scientific validation of the forensic science methods. Some of these methods include latent fingerprint analysis, bite mark analysis, microscopic hair analysis and firearms identification. This article critically examines the application of forensic evidence in criminal prosecutions and highlights the dangers of convictions based on a single piece of forensic evidence. The findings of recent reports, such as, the National Academy of Sciences (NAS) 2009 Report and President's Council of Advisors on Science and Technology (PCAST) 2016 Report, confirm the critical role and broad scope of these forensic pattern-matching methods. The reports also indicate flaws that affect the accuracy of these methods, such as, inadequate scientific validation, coincidental results (erroneous match), human, laboratory and interpretive errors etc. Therefore, this article argues that the court should follow a cautionary approach when relying on a single piece of forensic evidence and that strong corroboration with other forms of evidence linking the accused to the crime should be required.