Evidentiary Errors

Improper collection, labeling, or preservation of evidence, or the less than complete processing of a crime scene, can be the first steps in the road to conviction for an innocent person. Once the evidence reaches the lab, errors can multiply. Thousands of cases across the nation have recently been re-examined after serious problems were uncovered in forensic testing by state and municipal facilities, as well as by the FBI crime lab.

The same DNA evidence that is being used to exonerate the innocent is identifying the forensic “sciences” that were used in the past to convict the innocent. The reliability and evidentiary value of these procedures, including comparative bullet lead analysis, bite mark analysis, fingerprint analysis, microscopic hair comparison, and blood splatter analysis, have been called into serious question. Read the 2009 NAS report addressing these issues here.

One other aspect of forensic testing that cannot be overlooked is testing that has yet to be done. Advances in DNA technology have made possible the testing of rape kits and other biological evidence for conclusive proof of guilt or innocence. However, testing can not be conducted if the evidence is not properly collected and preserved.


Federal and/or state forensic science commissions should be established to address a wide range of issues including accreditation, training, standards in testing, independence of scientific testing, collection, preservation, destruction, and chain of custody of evidence. Additionally, the rigorous examination of scientific testing technique and testimony before a forensic expert takes the stand should be standard operating procedure for prosecutors and defense counsel. You can read North Carolina’s law regarding the proper preservation, testing, and destruction of biological evidence here.