The DNA Evidence May Not Save You.

The DNA Evidence May Not Save You

More than 330 people have been exonerated by post-conviction DNA testing, unequivocally proving their innocence. False confessions, a narrative admission to a criminal act that one did not commit, have been a contributing factor in approximately 25% of the DNA exoneration cases (The Innocence Project). For people who are wrongfully accused of a crime, pretrial DNA testing of blood, hair, saliva, semen, and other biological traces can serve as a valuable safeguard against wrongful conviction. Cases like that of Jeffrey Deskovic, however, suggest that confession evidence — even when false — may be persuasive enough to overpower exculpatory DNA. After a lengthy and manipulative interrogation, then-16-year-old Deskovic confessed to the rape and murder of a high school classmate. Prior to trial, DNA testing of the semen recovered from the victim excluded Deskovic as the perpetrator. Yet he was prosecuted and convicted by a jury. At trial, prosecutors theorized that the victim had prior consensual sex with an "unknown and unidentified boyfriend" and that Deskovic, who had confessed to rape and murder, killed her after failing to ejaculate. Deskovic was convicted in 1991 and released 15 years later when the DNA was matched to a convicted murderer who eventually pled guilty (Santos, 2006). In a legal system that purports to contain numerous safeguards to protect the falsely accused, the foregoing series of events may seem highly atypical. However, in 2010, The Center for Wrongful Convictions identified 19 cases in which confessors to rape and/or murder were tried and convicted despite having been excluded by DNA tests of key biological materials; since that time, additional cases have been reported and critiqued (Drizin & Riley, 2014; Goode, 2011; Martin, 2011). In arguing each of these cases, the prosecutor proposed a speculative theory to explain away the mismatched confession and exculpatory DNA. Although these case outcomes are counterintuitive, they are not surprising. Previous research shows that both confessions and DNA are highly persuasive forms of incriminating evidence. Yet, little research has compared contradictory self-report and scientific evidence in the same trial, and, when it has, the results have been mixed. Thus, in a recently published article in Psychology, Public Policy, and Law, Appleby and Kassin (2016) (PDF, 171KB) designed a series of studies to test people's perceptions of guilt in cases in which the scientific evidence (in the form of DNA) and the self-report evidence (in the form of eyewitnesses and confessions) contradict each other, a contradiction sometimes accompanied by a prosecutor's explanatory theory. Participants read a case summary about the rape and murder of a 16-year-old girl and the resulting police investigation. Study 1 varied the type of self-report (defendant statement or eyewitness), whether that self-report was incriminating or exculpatory, and DNA that was either incriminating or exculpatory. Studies 2 and 3 examined how people react to the same evidentiary contradiction (confession vs. exculpatory DNA) when the evidence was accompanied by the prosecutor's argument that the exculpatory DNA evidence merely indicated that the victim had prior consensual sex with an unidentified man. Participants rendered a verdict, rated their confidence in that verdict, estimated the likelihood that the defendant committed the crime, and rated how convincing of guilt they found each of the pieces of evidence. In Study 1, participants' perceptions of guilt were overwhelmingly influenced by whether the DNA results were incriminating or exculpatory; this preference was exhibited in verdicts, confidence ratings, and probability-of-commission estimates. In Studies 2 and 3, the introduction of a prosecutorial theory that sought to reconcile the apparent contradiction in the evidence significantly increased the conviction rate. Using an undergraduate sample, in Study 2, the introduction of a prosecutorial theory increased the conviction rate from 10% to 33%. Using a sample of community adults, Study 3 replicated these findings: a prosecutorial

A second means of countering the inherent power of confession evidence is to admit testimony from experts. At present, U.S. courts differ in their willingness to admit such testimony.