Post-Conviction DNA Testing and Wrongful Conviction

Originally posted on March 4, 2013

Over on Feminist Critics, Clarence linked to a piece The Spearhead featured concerning the wrongful conviction rate in homicide and sexual assault cases. The Post-Conviction DNA Testing and Wrongful Conviction report reviews sexual assault cases from from 1973 to 1987 in Virgina. The report found that between 8 to 15 percent of sexual assault cases resulted in wrongful convictions:

DNA testing produced a determinate outcome for 230 of these cases, in which there were 250 convicted offenders. In 56 of those convictions the convicted offender was eliminated as the source of DNA evidence, and for 38 convictions that elimination supported exoneration. Thus, we find that in Virginia cases resulting in a convicted offender between 1973 and 1987 where evidence was retained in an unbiased sample of 715 homicides and sexual assault convictions—

  • The convicted offender is eliminated as a contributor for a probative evidence item in 8 percent (n=56) of convictions.8
  • The convicted offender is eliminated as a contributor for a probative evidence item, and that elimination is supportive of exoneration, in 5 percent (n=38) of convictions.

For nonsexual assault homicide cases, a determinate finding about a convicted offender being a source of a DNA profile was reached in only 23 out of 293 convictions (8 percent), making it too rare to make declarative statements about the likelihood of potential wrongful conviction in those homicide convictions.

We find that DNA testing of items in these cases leads to a determinate conclusion in more than half of the sexual assault convictions (including homicides with a sexual assault). Thus, we focus much of our analysis on the sexual assault offenses. We find that in convictions in Virginia between 1973 and 1987 where evidence was retained in a sample of 422 convictions for sexual assault

  • The convicted offender was eliminated as the source of questioned evidence in 40 out of 422 convictions (9 percent).9
  • The convicted offender was eliminated as the source of questioned evidence in 33 out of 422 convictions (8 percent) and that elimination was supportive of exoneration.
  • The convicted offender was eliminated as the source of questioned evidence in 40 out of 227 convictions (18 percent) where a determination could be made from the DNA analysis.10
  • The convicted offender was eliminated as the source of questioned evidence in 33 out of 227 convictions (15 percent) where a determination could be made from the DNA analysis, and that elimination was supportive of exoneration.

The two most important numbers in the bullets above show the rate at which convicted offenders were eliminated as the source of questioned evidence and that elimination was supportive of exoneration. This occurs for 8 percent of all sexual assault convictions in the sample and for 15 percent of all sexual assault convictions where a determinate finding was made. We note again that additional facts about the case not included in the forensic file may ultimately include the convicted offender. However, given that these are sexual assault cases where the profile was determined to be male and excluded the convicted offender, we anticipate this will be relatively rare. (p. 5-6)

The researchers note two flaws with their results. One, the research did not include the context of the events. There may be other evidence that placed the convicted at the scene or there may have been a contextual reason why the DNA would not match. Two, the research only included cases with DNA evidence. Cases without it were not considered, meaning that it is possible that some innocent men were wrongfully convicted and yet have no means of proving that.

The latter is particularly important because many sexual assault cases either do not involve DNA evidence or the evidence is lost or destroyed following the conviction. We have no way of knowing how many of those cases resulted in wrongful convictions, and those innocent men must serve out the time with no hope justice or restitution.

The researchers were thorough in their methodology, breaking the data down into various subgroups. It is quite technical, and I think someone like Daran from Feminist Critics would have a better chance at explaining what it means than I would. The gist of the research is that of the 715 cases, 465 cases (65 percent) were indeterminate, neither inculpating or exonerating the convicted. Another 194 cases (27 percent) were inculpatory. Eighteen cases (3 percent) were exculpatory but insufficient to exonerate the convicted. The remaining 38 cases (5 percent) supported exoneration.

Later in the study, the researchers ask “What model predicts whether determinate DNA testing results on a conviction will be exculpatory or inculpatory regarding a convicted offender’s actual innocence?” Their findings:

All else equal, there were five significant predictors of whether determinate DNA testing of evidence from a sexual assault conviction (in Virginia in the 1970s/80s) yielded exculpatory evidence indicative of wrongful conviction, in the final multivariate predictive model. Specifically, as shown in Table 19—

  • More recent offenses were more likely to have an exculpatory DNA results, although we note that the difference in the averages was only two years.
  • Sexual assault convictions for which enzyme typing was done were significantly less likely to yield exculpatory DNA testing results. As noted previously, enzyme typing increased the specificity of forensic serological tests, especially when combined with ABO typing results, meaning that stronger conclusions about a convicted offender’s inclusion as the source of forensic evidence could have been made prior to the original conviction.
  • Convictions for both murder and sexual assault were more likely to yield exculpatory DNA results than were convictions for sexual assault alone. This finding is difficult to explain, given that greater amounts of physical evidence were likely available in murder and sexual assault cases than in those involving only sexual assault.
  • Sexual assault convictions for offenses that occurred indoors, such as inside the victim’s or convicted offender’s home, were significantly more likely to yield exculpatory DNA results. Although untestable in the current data set, this relationship may be indicative of the lack of reliable eyewitness testimony in such cases. The crime descriptions for many indoor sexual assaults indicated that they frequently occurred at nighttime (in the dark) and involved only the victim and convicted offender and no other potential witnesses.
  • The more suspects convicted for a sexual assault, the more likely any individual suspect’s conviction was to have exculpatory DNA results. 9 (p. 47-48)

Curiously, the above research shows that the factors false allegation advocates are concerned about are the very factors most likely to result in wrongful convictions. The researchers presented case studies (p. 52) to illustrate the three types of results–inculpatory, exculpatory but insufficient, and exculpatory–and again those cases match the kinds of cases that false allegation advocates complaint about.

This is important because many of those opposed to discussing false allegations and wrongful convictions argue that the advocates are crazy and exaggerate the cases. However, the above research shows that their complaints are dead on. These are the kinds of cases we must be concerned about.

The researchers also addressed the large number of indeterminate cases in their conclusions, and in case anyone thinks that they will err on the side of those shouting “those men are guilty, guilty, guilty!” think again:

Logically, there are three possible outcomes for the convictions with indeterminate results. First, it is possible that the 38 convictions with probative evidence that eliminates the convicted offender as the source include all of the convicted offenders who would have been eliminated had a determinate result been obtained. Second, it is possible that there are others who had indeterminate results who would have been eliminated as the contributor of probative evidence had a determinate result been obtained.[…] Third, it may be the case that the cohort with a determinate result effectively approximates a random sample of all convictions, and thus it is appropriate to interpolate the determinate results on to the convictions with indeterminate results. There is a fourth possible outcome, that the convictions with determinate results underestimate the rate of elimination in the convictions with indeterminate results.[…] Given the differences in the yield of physical evidence […] described in Table 6, it seems likely that the answer lies in the second option, somewhere between the two extremes. (p. 57)

The researchers admit that they could extrapolate the potential variables, and yet chose not. However, they state:

We note that a standard question in social science is whether an observed outcome is large or not. In this case, given that even our most conservative estimate of exclusion in support of exoneration is larger than previous estimates, we believe our result is unquestionably a large number. Even our most conservative estimate suggests that 8 percent (or more) of sexual assault convictions in a 15-year period may have been wrongful. That means hundreds, if not more than a thousand, convicted offenders may have been wrongfully convicted. (p. 58)

They also note that as a result of this, hundreds of victims did not have their cases actually solved. By proxy, this also means hundreds of actual offenders remain free to harm others. While that is very important and worth noting, the greater moral injustice is that innocent people who committed no crime have their freedom taken from them, and not just for a couple of days or months, but for years, sometimes even decades, and are also painted as sex offenders and rapists, labels that will stick despite their exoneration.

As a civilized society, we should find an 8 to 15 percent wrongful conviction rate appalling, yet we do not. We show little concern about this issue on the broader social level, even when we hear about men spending two or three decades in prison for a crime they did not commit (and in some instances crimes that never happened). Feminists in particular argue against raising concern about false allegations and wrongful convictions.

That helps no one, particularly not the innocent people locked in prison. We need to start looking at the factors that prompt wrongful convictions. Our zealousness to lock up the offender may cause us to overlook flaws in the accuser’s story, flaws in the investigators’ methods, and our own attitudes about the those charged with crimes. We also need to look at our court and prison systems and ask whether these systems are set up to convict and imprison regardless of a person’s innocence or whether they are actually places of justice. An 8 to 15 percent wrongful conviction rate suggests the former when it should be the latter.


2 thoughts on “Post-Conviction DNA Testing and Wrongful Conviction

  1. Hey!
    Thanks for the post, TS 🙂
    No comments as of yet (not counting this one) but honestly, to disagree, someone would have to be willing to do alot of work, and I suppose most wouldn’t rather pat you on the back.
    But I will. It’s important to realize that the amount of false convictions in this country is often insane, and the cjs needs extensive repair.

  2. Pingback: Texas SC to Study Wrongful Convictions | deafinprison

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