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Report Finds Bad Forensic Evidence Leads to More Wrongful Convictions and Establishes Forensic Errors Typology

by Matt Clarke

The National Institute of Justice and independent research consultant Dr. John Morgan collaborated “to analyze and describe the impact of forensic science on erroneous convictions that the National Registry of Exonerations classified as being associated with ‘false or misleading forensic evidence.’ … Findings from this work led to the development of a forensic error typology, or codebook, which categorizes factors related to misstatements in forensic science reports [Type 1], errors of individualization or classification [Type 2], testimony errors [Type 3], issues related to trials and officers of the court [Type 4], and evidence handling and reporting issues [Type 5].”

“In his examination, Dr. Morgan analyzed 732 cases and 1,391 forensic examinations from the National Registry of Exonerations. The dataset included examples from 34 forensic disciplines, including serology, forensic pathology, hair comparison, forensic medicine, seized drugs, latent prints, fire debris, DNA, and bitemark comparisons.”

Of the 732 cases examined, 635 had errors related to forensic evidence. The 1,391 forensic examinations included 891 with errors related to forensic evidence. At 100% of the 130 examinations analyzed, seized drug analysis was the examination with the highest percentage of Type 2 errors. It was followed by pediatric physical abuse (83% of cases had forensic errors with 22% having Type 2 errors out of 60 cases analyzed), fire debris not including chemical analysis (78% of cases/38% Type 2 in 45 cases), bitemark comparison (77% of cases/73% Type 2 in 44), pediatric sexual abuse (72% of cases/34% Type 2 in 64), serology (68% of cases/26% Type 2 in 204), shoe/foot impressions (66% of cases/41% Type 2 in 32), DNA (64% of cases/14% Type 2 in 64), hair comparison (59% of cases/20% Type 2 in 143), and blood spatter (58% of cases/27% Type 2 in 33).

“Most errors related to forensic evidence were not identification or classification errors.” The most common errors made by forensic scientists were associated with incompetent or fraudulent examiners, “junk science,” or organizational deficiencies in training, management, governance, or resources.

Most serology errors were related to blood typing and characterized by testimony errors, best practices failures, and inadequate defense. Most hair comparison errors “conformed to the standards recognized at the time of the trial but would not conform to current standards.”

Almost all latent fingerprint errors “were associated with fraud or uncertified examiners who violated basic standards.” Most gunshot residue errors were due to testimony that “did not clarify the limits of that analysis such as the possibility of secondary transfer and uncertainties of interpretation.”

DNA errors were “often associated with identification and classification errors. Most commonly, labs used in early DNA methods that lacked the ability to apply the testing or interpretation in a reliable way. DNA mixture samples were the most common source of evidence interpretation error.”

All but one of the seized drug errors were due to errors using field testing kits, not lab errors. Most bitemark errors were associated with “independent consultants outside of forensic science organizations.”

Dr. Morgan cautioned against cognitive bias in forensic testing and suggested that the discovery of errors be accompanied by a follow-up analysis similar to that done in “higher reliability” fields such as air traffic control. He noted that wrongful convictions were often associated with poorly validated standards, overly complex analysis, and reliance on presumptive tests.  


Source: National Institute of Justice

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