A blog of the Philadelphia Bar Association’s Criminal Justice Section

By Marissa Boyers Bluestineimgres

Legal Director, Pennsylvania Innocence Project

Last week, Pennsylvania became the 48th state to allow experts in human memory and recall to testify at trials involving cases built upon eyewitness testimony. The decision in Commonwealth v. Walker (28 EAP 2011) reversed the Commonwealth’s longstanding per se prohibition against such testimony, choosing instead to “join the vast majority of jurisdictions which leave the admissibility of such expert testimony to the discretion of the trial court.”


The majority opinion, written by Justice Todd, focuses on the unique difficulties that eyewitness identifications pose in the criminal justice system: short of a confession, no other piece of evidence is as persuasive as an eyewitness or victim who looks at the defendant and says “that’s the one.” Yet, at the same time, the Court points out that “eyewitness identifications are widely considered to be one of the least reliable forms of evidence.” Compounding the problem, according to the Court, is that jurors often are unaware of the complexities of human memory and the counterintuitive notions involved in creating and storing a memory. Because the proffered expert testimony would not speak directly to whether particular witnesses are or are not reliable in their observations, the Court ruled that the evidence “provides jurors with education by which they assess for themselves the witness’s credibility … with full awareness of limitations that eyewitness testimony may present.”


Moreover, the Court addressed the argument that cross-examination and closing arguments are sufficient to educate jurors as to the vagaries of eyewitness identification. Because eyewitnesses present as “neutral, credible, and confident” before a jury, there is a danger that without the tool of expert testimony the jury may “overestimate the veracity and reliability of eyewitness identification.” In fact, cross-examining a witness as to the issues related to human memory, said the Court, “would not be within the permissible scope of cross-examination.”


For all of these reasons, the majority ruled that “an absolute ban on expert testimony in this area is no longer the best approach in determining how to assist the finder of fact where mistaken identification is at issue. … Thus, we believe that it is time to take the step of joining those jurisdictions which allow the admission of expert testimony on relevant factors concerning eyewitness identification, at the discretion of the trial court, subject to an abuse of discretion appellate standard of review.”


The Court held that the testimony would be admissible under Rule 702 (permitting court approved experts to offer opinions otherwise impermissible) insofar as the information is beyond the knowledge of an average layperson and would assist the trier of fact to understand the evidence. However, since the case before the Court did not have a specific ruling as to whether the methodology of the subject of the expert testimony “has general acceptance in the relevant scientific community,” the case itself was remanded to the trial court for a Frye hearing. The Court was careful to limit its ruling only to areas involving eyewitness identification, and not other areas of recognized social science, leaving the core holding of its precedents Commonwealth v. Spence, and Commonwealth v. Simmons otherwise intact. Even if the testimony is found to have been “generally accepted,” anyone proffering expert testimony at trial must still make an on-the-record offer of proof to the court including (1) how the expert’s testimony is relevant to the identifications, and (2) how the testimony will assist the jury pointing to specific factors (e.g., stress, weapons focus, cross-racial identifications) that could impair the accuracy or reliability of an eyewitness.

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