Forensic Source Conclusions: Twenty Threats to Validity

Forensic science evidence may be the most powerful weapon in the arsenal of law enforcement officials and prosecutors. As such, it is important to be aware of factors that threaten the validity of forensic source conclusions (e.g., “This bullet was fired from that gun”). This paper identifies 20 threats to the validity of forensic source conclusions including threats that spring from: (a) the evidentiary samples themselves, (b) forensic examiners and the procedures they use, (c) features of the law, and (d) cognitive limitations of jurors and others who must weigh forensic science source claims.