The Case of Troy Davis: What DNA Exonerations Can Teach Us about Wrongful Convictions
When someone is wrongfully convicted of a crime they lose years of their lives to unjust sanctions, the perpetrator is free to continue victimizing others, and if it happens too often society loses faith in the criminal justice system. With the advent of DNA analysis some of this faith has been lost, because a sizeable number of death row DNA exonerations have made it clear that innocent men and women have been executed in the past. In an effort to better understand how a person might be wrongfully convicted the case of Georgia death row inmate Troy Davis is analyzed here. The prosecution's case was almost completely dependent on eyewitness testimony, despite scientific evidence showing this type of evidence is often unreliable. During the trial it emerged that the police may have used coercive methods on some witnesses, conducted flawed photo lineups, and likely developed 'tunnel vision'. Despite these shortcomings, and a significant number of recantations by several of the prosecution's witnesses, the 11th Circuit Court upheld the original conviction in 2010. All subsequent appeals for relief were denied and Troy Davis was executed on September 21, 2011.
The Case of Troy Davis: What DNA Exonerations Can Teach Us about Wrongful Convictions
After spending nearly 25 years in prison for aggravated rape, Robert Clark was exonerated using DNA evidence and then ordered released by a Cobb County Superior Court Judge in Georgia on Thursday, December 8, 2005 (The Innocence Project, 2005). The crime scene DNA was then used to search the CODIS DNA database for possible matches and Tony Arnold was identified as the perpetrator. Despite statements to the police by Clark and another witness that placed Arnold in the victim's car a few days after the rape, Arnold was never investigated as a possible suspect. Aside from the injustice of Clark losing nearly 25 years of his life to a wrongful conviction, Arnold was free to commit at least three more rapes between 1986 and 1995.
Concern over the prevalence of wrongful convictions therefore isn't just about sending innocent persons to prison, but also about preventing future crimes. If the rate of wrongful convictions is perceived to be too high then public trust in the justice system would be also undermined. With 273 DNA-mediated exonerations since 1989 (The Innocence Project, 2011), resulting in 16 states imposing a moratorium or outright bans on the death penalty, it seems that confidence in the justice system has already eroded enough to question the use of the death penalty (Schwartz and Fitzsimmons, 2011). The true prevalence of wrongful convictions will probably be impossible to determine, since most don't involve DNA evidence or serious crimes, but reliable estimates are essential for energizing the public to push for the necessary reforms to reduce wrongful conviction rates.
The Prevalence of Wrongful Convictions
Estimating the prevalence of wrongful convictions is a methodological and political nightmare, as suggested by the results of a recent study. Zalman, Smith, and Kiger (2008) surveyed police chiefs, prosecutors, defense attorneys, and judges in Michigan for their perceptions about how common wrongful convictions were in their jurisdictions. The final overall estimate was 1-4%, despite significant disparities between the four groups.
The 1-4% wrongful conviction rate is significantly different from the 1/2% error rate arrived at approximately 20 years earlier by a similar study conducted in Ohio (reviewed by Zalman, Smith, and Kiger, 2008). The discrepancy between the two surveys were interpreted as a reflection of increasing official recognition that wrongful convictions do exist, thanks in large part to the successful use of DNA to obtain exonerations. Despite this growing awareness, nearly 20% of all respondents in the 2005/2006 survey still believed that wrongful convictions did not occur in their own jurisdictions (Zalman, Smith, and Kiger, 2008). The demographics that constituted the nonbelievers were police chiefs (41.0%), prosecutors (47.8%), and judges (5.3%), but not defense attorneys. Suspects and the accused therefore have good reason to fear the criminal justice system, not only because they will be rightfully sanctioned for any crimes they may have committed, but because the self-confidence police and prosecutors have in their ability to determine guilt or innocence has been proven to be unwarranted. The possibility that one jurisdiction will somehow be exempt from wrongful convictions when compared to others is also not credible, since the 273 DNA exonerations have occurred in 34 states (The Innocence Project, 2011).
Another way to assess the prevalence of wrongful convictions is to examine how often DNA evidence excludes potential suspects. A 1995 study examined the exclusion rates in 13 state and local laboratories, 4 private laboratories, an armed forces laboratory, and the FBI laboratory (Connors, Lundregan, Miller, and McEwen, 1996, pp. 20-21). Of the combined 21,621 DNA samples analyzed, close to 23% (~5,000) of suspects were excluded and an additional 16% (~3,460) was inconclusive because the crime scene DNA was of poor quality. Although a percentage of these exclusions probably represent the use of DNA as an investigation tool, it also reveals how often the police were wrong about a suspect's potential culpability.
Additional evidence of how often police investigators are wrong about a suspect's guilt was provided by studies showing professionals who are required to judge the guilt or innocence of a suspect based on an interview, such as polygraphers, detectives, and customs inspectors, were accurate only 45-60% of the time (Kassin and Gudjonsson, 2005, p. 27).
With 273 DNA exonerations over the past 22 years for only the most serious crimes and only in cases where DNA evidence was available, a 23% exclusion rate in forensic laboratories, and a mean accuracy rate of 54% when judging the guilt or innocence of a suspect based on an interview alone, the estimated 1-4% rate of wrongful convictions probably represents an underestimate.
Causes of Wrongful Convictions
DNA-mediated exonerations provide a unique opportunity to examine the causes of wrongful convictions, because they represent actual innocence rather than legal innocence. Legal innocence results from procedural errors or evidence that fails to overcome reasonable doubt in a fair courtroom, regardless of whether the accused is guilty or innocent. Overturning convictions of the legally innocent often depends on a subjective analysis of the court proceedings during an appeal (Zalman, Smith, and Kiger, 2008, p. 75). In contrast, exonerations based on DNA evidence are objective in nature because this type of evidence is capable of ruling out the possibility that the convicted person committed the crime.
The 273 wrongful convictions that were eventually overturned after DNA evidence was analyzed, resulted from the jury giving eyewitness testimony too much weight (75%), improper forensic evidence presentation or interpretation (50%), false confessions or incriminating statements (25%), and informant testimony (19%; The Innocence Project, 2011).
In Robert Clark's case, the danger of relying too heavily on eyewitness testimony is readily apparent. Research studies have shown that eyewitness testimony is often unreliable (reviewed by Shay, 2009, pp. 1526-1528; Gould and Leo, 2010, pp. 841-843). Having the witness inspect a photo of the suspect in the absence of other photos, having only one person in the lineup, engaging the witness in photo or lineup sessions multiple times, or coaching before or during the lineups, have all been shown to bias the witness. Ideally, the witness should inspect multiple photos or multi-person lineups only once and in the absence of any instructions or discussions. Scientists have concluded that any statements made in a courtroom that differ from those made during the original identification session should be taken with a grain of salt, because they could be the product of coaching, whether intentional or not.
The use of informants to implicate a suspect or defendant in a crime is considered by some legal experts to be at best a questionable practice (reviewed by Gould and Leo, 2010, p. 851-852). Informants are often members of the criminal class and given rewards for their testimony, so it should come as no surprise that informant testimony played a role in 25% of the wrongful convictions later overturned by DNA evidence.
Until DNA analysis became common practice in forensic laboratories, the analysis and use of other forms of forensic evidence often depended on methods that had never been validated scientifically (Gould and Leo, 2010, pp. 852-854). The 'hard' evidence that DNA analysis now provides casts these older methods in an unfavorable light, including the mainstays of forensic investigations, such as latent fingerprint, hair, and blood type analysis. Recent studies have shown that these forms of evidence lack the rigor required for courtroom evidentiary proceedings. In addition to a Maryland judge declaring latent fingerprint analysis not credible enough to enter the courtroom, the National Research Council has called forensic science in the United States inconsistent enough to lack credibility. This state of affairs is only made worse when the occasional report of forensic malfeasance occurs. All evidence and testimony coming out of a forensic laboratory should therefore be…