Commonwealth v. Walker

Brief Filed: 8/11
Court: Pennsylvania Supreme Court, Eastern District
Year of Decision: 2014

Read the full-text amicus brief (PDF, 84KB)


Expert Testimony regarding the reliability of eyewitness identification

Index Topic

Eyewitness Identification


This case involves a gunpoint robbery of two students in the early morning hours. One of the victims was hit with the gun and injured; the other was able to get away quickly. The victim who had been struck identified the Petitioner as the perpetrator from a photo array, and the other was not able to make certain identification. At trial, only one victim was able to positively identify the Petitioner as the one who had committed the robbery. The crime occurred in poor lighting, was brief, involved a gun and was committed by an individual of a different race than the victims. Motions raised pre-trial asked the court to allow for an expert to testify to those issues, for appropriate jury instructions and for limiting instructions on argument. All motions were denied, and the Superior Court affirmed the decisions on appeal. The Pennsylvania Supreme Court has long held that expert testimony from social scientists in the fields related to eyewitness identification — human memory, perception and recall — is improper as it intruded on the jury’s duty to judge the “credibility” of each witness. The Pennsylvania Supreme Court accepted the case for review on two grounds: “(1) whether the trial court should have had the discretion to allow the Petitioner to present expert testimony regarding human memory, perception, and recall, and (2) whether the Court permit expert scientific testimony, whether it be for the defense or prosecution, on how the mind works as long as the testimony has reached general acceptance”. In a nutshell, at the heart of the case is the issue of admissibility in Pennsylvania courts of expert testimony on research regarding the reliability of eyewitness identification.

The research base that forms the foundation for eyewitness memory is extensive (e.g., reliability of eyewitness identification, factors affecting the reliability of eyewitness identification, etc.). Given that the well-established expert testimony regarding human perception, memory and recall in cases involving eyewitness identification is generally accepted in the field and that the overwhelming response of courts nationally is to allow such testimony, it was determined that APA would file a brief to educate the court on this matter. Specifically, because many of the variables affecting eyewitness identification are counter-intuitive and simply unknown to the layperson, not admitting expert testimony in this regard could result in mistaken convictions.

APA's Position

On Aug. 1, 2011, APA filed an amicus brief urging the court to follow the majority of other states and allow expert testimony on the strong body of psychological research regarding eyewitness testimony, including research regarding juror misunderstanding of the accuracy of eyewitness identification and the factors that can affect the accuracy of eyewitness identifications. The brief also explains that the means by which this research has been undertaken and the results have been widely accepted in the scientific community.


On May 28, 2014, the state’s highest court reversed prior precedent that barred expert testimony on the social science research regarding factors that affect the reliability of eyewitness testimony.

In reaching its decision, the court cited APA’s brief on each of the following points: 1) most jurors do not understand the factors that affect reliability of eyewitness testimony, making expert testimony important; 2) experts would speak to objective scientific research regarding eyewitness identification, not factual issues within the jury’s purview; 3) research shows that juries do not abdicate their fact finding responsibility when presented with expert testimony; 4) this area of research has general acceptance in the scientific community — specifically that extensive research has been conducted on human memory and its limits, as well as inaccurate eyewitness identification; and 5) published research has identified numerous factors that impact the reliability of eyewitness identification.