The Evolution of Exonerations and DNA Science


By Emily West, Innocence Project Research Director

DNA science has improved steadily over the last two decades — and the number of DNA exonerations has grown in tandem.A new article I wrote with two Innocence Network colleagues explores the changing nature of DNA evidence in recent years and examines the types of evidence that led to exonerations. “The Genetics of Innocence: Analysis of 194 U.S. DNA Exonerations,” which appears in The Annual Review of Genomics and Human Genetics, was written by Innocence Project Staff Attorney Olga Akselrod, Boise State University Professors Greg Hampikian and myself.

The article provides a brief overview of the history of the different types of DNA testing methods used to exonerate and some interesting findings in trends over time in testing—how earlier methods became obsolete as newer, more advanced methods became available and how the increase in exonerations over time parallels the advances in methods.  We also present what types of evidence led to exonerations—the most common being swabs from rape kits (65%) and clothing associated with the crime (53%). 

The article then goes into greater detail  to examine how many cases relied on more than one type of testing method (i.e. a combination of STR and Y-STR testing) or on more than one piece of evidence (i.e. both the victim’s clothing and fingernail evidence yielded exculpatory results).  Also presented are the types of testing used on various pieces of exculpatory evidence.  For example, there were nine cases where fingernail evidence yielded exculpatory results, most often using STR testing alone.  However, in all nine of these fingernail cases, there was at least one other piece of evidence involved which provided further exculpatory evidence. 

There are many more interesting findings in this article, including an overview of demographic information about the exonerees and the contributing causes involved in their cases, a presentation of valid and invalid forensic testimony used at the exonerees’ original trials, and case profiles which provide context to the types of testing and evidence used to exonerate.

Read the article abstract or download the full article

(a subscription is required for the full article).


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