DNA Testing and Post-Conviction Exoneration

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Since the early 1990s, nearly 200 felony convictions have been overturned in the US. This paper will examine the near revolutionary role DNA testing has played in such convictions. It will also seek to examine why such individuals suffered from initial wrongful convictions. This paper will be divided into three sections. The next section will provide a brief overview of the growth of exoneration organizations. The third section will review the research related to wrongful convictions and the role of DNA post-conviction testing in exonerations.


It's been understood for decades that many individuals have been wrongfully convicted of crimes. Indeed, this understanding prompted the emergence of organizations, such as Centurion Ministries and the Innocence Project to initiate the process of post-conviction testing (Hampikian, West, & Akselrod, 2011). The need for a post-conviction overview of felony cases is mainly due to a growing understanding that the methods used to achieve conviction lacked true scientific merit. Centurion Ministries was begun by James McCloskey, an ex-Wall Street executive and lay minister in 1983, years before DNA testing was widely used. Conversely, the Innocence Project was founded in 1992 by lawyers Barry Scheck and Peter Neufeld. This organization is affiliated with Yeshiva University's Benjamin N. Cardozo School of Law.

The purpose of both organizations is reform of the criminal justice system to exonerate wrongfully convicted individuals and to prevent future such wrongful convictions from occurring again. The advent of legally accepted DNA testing led to a proliferation of similar organizations and legal clinics throughout the US and many of them joined to form the Innocence Network in 2005. The Network seriously considers and investigates any claims of innocence from convicted felons (Hampikian, West, & Akselrod, 2011). The total number of Innocence Network Projects has reached several dozen, of which the vast majority is in the US.

The first individual convicted using DNA testing in the US was Tommie Lee Andrews in 1987. His case established the admissibility of DNA evidence to obtain a lawful conviction. There were legal challenges to the use of such evidence during the 1980s and 1990s. However, by the mid-1990s, the use of DNA had become firmly established with wide agreement on its efficacy in the scientific and legal communities (Hampikian, West, & Akselrod, 2011). Of course, there may continue to be challenges to the use of DNA. However, these challenges have more to do with potential abuses of the investigative procedure, than with the legitimacy of the technology itself.

Wrongful Conviction and the Need for Post-Conviction Oversight

The existence of roughly 200 cases of exoneration by DNA evidence indicates there are some serious procedural and evidentiary issues in the criminal justice system. Indeed, the traditional pre-DNA era methods of establishing guilt or innocent have for many years been found lacking in true scientific credibility. There are four commonly used methods to establish wrongful guilt. The first and most widely reported method has been the misidentification of the suspect, which occurs in three-quarters of all such cases (Hampikian, West, & Akselrod, 2011). It's notable that victim misidentification of the perpetrator occurs in nearly two-thirds of cases overturned by DNA testing as well.

The second problematic evidentiary data is the use of false confessions, which would include both pleas and admissions. Such improper confessions were found in 30 percent of exoneration cases in the study conducted by Hampikian et al. (2011). False confessions also include the dubious use of jailhouse informant testimony. The uncritical use of this type of information was the basis for more than one-fifth of the wrongful convictions.

The third is the use of forensic scientist testimony, of an invalid nature, to obtain convictions in as many as 146 trials. It's notable that in each of these trials, reliable forensic information or transcripts were available. But these data sources were not used for investigative analysis (Hampikian et al., 2011). Invalid forensic testimony covers such areas as serology in 38 percent of the cases, hair comparison in 22 percent, fingerprint evidence in 2 percent and teeth mark comparison in 3 percent. In over 40 percent of the DNA related exonerations, the actual perpetrator was correctly identified using DNA analysis. Each of these factors will be examined in brief next.

Serology is the examination of human blood, saliva, semen and vaginal secretions. It's also the most used form of testimony in rape or rape-murder cases. Hampikian et al. (2011) report that over 60 percent of the serology testimony examined for their paper was not proper evidence. Serology is prominently featured in post-conviction exoneration cases and this greatly emphasizes the high level of errors using this methodology (Garrett & Neufeld, 2009).

Hair comparison or microscopy is the next most widely used form of testimony and research has found that nearly half of such evidence was erroneous. Hair comparison involves collecting hair samples from the victim and suspect. A visual comparison is then made between the two samples (Hampikian et al., 2011). However, hair comparison often involves the dubious use of statistics to establish guilt. This is because the methodology has never been subjected to a systematic scientific evaluation to determine whether its conclusions, regarding hair type incidence, are in fact valid and reliable. This negates any positive assessment that a hair sample definitively originated from an individual. Moreover, some forensic experts have been found greatly exaggerating the evidentiary value of such evidence (Garrett & Neufeld, 2009). Thus, it's not possible to make any positive identification using this method.

Fingerprints are the one area of pre-DNA era forensics that has been found to have a solid track record of positive identification. This is not to argue that abuses can't occur with such a methodology. An example of abuse occurred when police neglected to testify that fingerprint evidence exists that can exonerate a wrongfully convicted individual (Hampikian et al., 2011). However, in nearly 85 percent of cases reported by the authors (2011), where fingerprinting was used, this method was found to have been properly used and applied.

Teeth marks are particularly controversial in the forensic science community. This method rests on the assumption that every individual's bite mark pattern is different (Hampikian et al., 2011). However, this assumption lacks a firm statistical foundation. However, experts in the field have been found giving testimony that exaggerates the evidentiary value of such patterns. There is a notable case of a wrongful conviction involving an individual who only had four upper teeth. His conviction occurred even though the victim's bite mark pattern clearly demonstrated six upper teeth.

There remains one area of wrongful conviction that remains a puzzle and requires some further explanation. This is when completely innocent individuals confess to crimes they didn't commit. Confessions of this type are generally accepted by the public under the mistaken notion that innocents don't confess to committing crimes. However, this view is largely ill-informed of the process by which police obtain confessions. Indeed, there is a considerable body of research which demonstrates that some innocents, out of fear, low intelligence, or sheer naiveté, make false confessions (Drizon & Leo, 2004; Kassin, 2008; Kassin, Drizin, Grisso, Gudjonsson, Leo, & Redlich, 2010). The factors that can extract false confessions include being falsely held by police and interrogated for several hours. Police interrogation procedures often incorporate threats of life in prison or even the death penalty if a suspect doesn't submit a confession. The growing DNA exoneration movement has shown that such false confessions are not unusual. They have been found to occur often in the face of unscrupulous police intimidation tactics, deception and persuasion.

There are several key factors involved in post-conviction exoneration by DNA. First, for many cases, the identity of a perpetrator is at issue when a crime has been committed. Second, the evidence that can be used to overturn a wrongful conviction is almost always collected at the crime scene (Hampikian et al., 2011). However, this crucial data may not always have been preserved and thus may be unavailable when needed in post-conviction reviews. Third, human testimony is notoriously unreliable, particularly the further in time one moves on from the time of the incident. However, it's just this type of testimony that is most relied upon to establish an individual's guilt. It should be noted that confessions given under extreme duress, are notoriously unreliable. Fourth, false convictions can result from scientific comparisons (such as blood type) unless properly analyzed within a statistical context. Finally, investigators must be properly trained to always use the scientific method. This means they must reject any theory that does not comport with the available evidence.

By the summer of 2011, an estimated 272 Americans were wrongfully convicted and then later exonerated through proper use of DNA evidence. The use of methodologies lacking in scientific rigor appears to have been implicated in each of these cases. It should also be noted that wrongful convictions extract a serious social cost (Hampikian et al., 2011). That is, a perpetrator in each of these wrongful convictions remains free to commit additional crimes. These true criminals sometimes do so with an escalating degree of brutality and violence. Therefore, it's incumbent upon public policymakers to verify the correct individuals have been arrested and incarcerated.


Drizon, S., & Leo, R. (2004). The problem of false confessions in the post-DNA world. North Carolina Law Review, 82, 891–1007.

Garrett, B., & Neufeld, P. (2009). Invalid forensic science testimony and wrongful convictions. Virginia Law Review, 95, 1–97.

Hampikian, G., West, E. & Akselrod, O. (2011). The genetics of innocence: Analysis of 194 U.S. DNA exonerations. The Annual Review of Genomics and Human Genetics, 12, 97–120.

Kassin, S. (2008). The psychology of confessions. Annual Review of Law and Social Science, 4, 193–217.

Kassin S., Drizin, S., Grisso, T., Gudjonsson, G., Leo, R. & Redlich, A. (2010). Police-induced confessions: Risk factors and recommendations. Law and Human Behavior, 34, 3–38.