The Pennsylvania Supreme Court recently decided two cases that address whether parties can use expert witnesses to help juries assess lay witness testimony. In one case, Commonwealth v. Walker (2014), the court lifted a ban on the admissibility of expert testimony regarding eyewitness identification. In the other case, Commonwealth v. Alicia (2014), the court held that expert testimony regarding false confessions was inadmissible.
Although the two outcomes diverged, robust research suggests that eyewitness identification and false confessions pose significant problems for the legal system (Wells et al., 1998; Kassin et al., 2010). So, how did the court justify its differing opinions? And what lessons can be learned from these discrepant decisions concerning how social science can influence legal decisions?
In Walker, the defendant was convicted of robbery after being identified by the victims. The trial court denied the defense's request to offer expert testimony on the unreliability of eyewitness testimony, citing Pennsylvania case law banning such testimony on the grounds that it would give experts the appearance of authority concerning witness credibility. On appeal, the Pennsylvania Supreme Court overturned the ban, relying upon a significant body of research that highlights the limits of human memory and poor reliability of eyewitness testimony. The court also noted that many jurisdictions across the United States are accepting expert testimony on eyewitness identification.
In Alicia, a suspect confessed to murder after six hours of interrogation, and the defense proffered expert testimony that his confession might be false. The trial court allowed the expert to testify about false confessions generally, but prevented him from discussing it in the context of this case because the defendant never alleged police coercion led to a false statement. On appeal, the Pennsylvania Supreme Court deemed such expert testimony inadmissible, relying on Pennsylvania case law holding that juries are capable of determining whether a witness is lying.
The two cases concern issues of serious consequence in the criminal justice system: eyewitness identification and false confessions. Research has established the unreliability of eyewitness testimony and the ease by which false confessions can be generated, particularly when under duress or in cases of diminished mental capacity. Further, the number of wrongful convictions based on faulty eyewitness testimony and false confessions is alarming. Of the 1,432 exonerations in the National Registry of Exonerations, over 33 percent of wrongful convictions were due to mistaken identity and over 10 percent were due to false confessions (see The National Registry of Exonerationsopens in new window). Why then did the Pennsylvania Supreme Court attempt to alleviate the problem of faulty eyewitness identification, but not the problem of false confessions?
Several explanations seem likely. First, most judges are not scientists and humans tend to be more accepting of things we understand. Judges may easily understand how an individual's perception and memory might be distorted when under duress, but it may be more difficult for them to understand people admitting to crimes they did not commit. Second, absent blatant abuse, courts often defer to police in terms of how investigations are conducted, believing that the adversarial system will "find the truth." With no allegations of police coercion in Alicia, the court had no reason to consider false confessions. This contrasts with Walker, in which the issue of eyewitness identification was directly relevant to the court's decision. Third, eyewitness identification and false confession present inherently different issues to the jury. Although both are concerned with testimonial reliability, eyewitness identification is concerned with witness accuracy, while false confession is concerned with witness honesty. Judges may believe that jurors need guidance in the former instance in terms of assessing the limits of human perception and memory, but not in the latter instance.
These explanations may help make sense of the discrepant decisions in Walker and Alicia, but the fact remains that an established research base was applied differently in these two cases. This poses two problems. First, it sets no guidelines for how social science research should be applied in court. Second, it suggests that the application of social science research is being left to the whims of judges. The solutions? Increasing judges' understanding of social science research and perhaps standardized intra-jurisdiction application of this research. How best to accomplish these goals? It seems the jury's still out on that.
