## Facts

- Benjamin Walker was charged in Philadelphia with two separate armed robberies of college students occurring about two weeks apart in October 2005.
- The first robbery occurred around 1:00 a.m. on October 15, 2005, when three Drexel University students were approached at gunpoint and robbed of phones and cameras; two later identified Walker from photo arrays, and one identified him in a lineup.
- The second robbery occurred around 3:00 a.m. on October 28, 2005, when two University of Pennsylvania students were approached by two assailants, forced to the ground at gunpoint, robbed, and one victim was struck with the gun; one victim later identified Walker from a photo array and the other was less certain.
- The only evidence linking Walker to the charged offenses was eyewitness identification under conditions including late-night lighting, stress, and presence of a weapon.
- Before trial, Walker sought to present expert testimony on factors affecting eyewitness reliability and requested a Frye hearing; the trial court denied both and excluded the expert.
- The jury acquitted Walker of charges tied to the first robbery but convicted him of charges tied to the second robbery; he received an aggregate sentence of 17½ to 35 years’ imprisonment.
- The Superior Court affirmed, applying Pennsylvania precedent that categorically excluded expert testimony on eyewitness identification as invading the jury’s credibility function.

## Issues

1. Whether Pennsylvania law should continue to categorically bar expert testimony concerning the reliability of eyewitness identification.
2. Whether trial courts may, in their discretion, admit expert testimony on general factors affecting eyewitness accuracy without invading the jury’s role.
3. Whether, when such testimony is proffered, trial courts may conduct Frye proceedings to assess general acceptance of the expert’s principles and methodology.

## Decision

- The Supreme Court of Pennsylvania reversed the Superior Court.
- The Court abolished the per se ban on expert testimony regarding eyewitness identification.
- The Court held that admissibility is left to the trial court’s discretion under ordinary evidentiary standards.
- The Court remanded for the trial court to reconsider Walker’s proffered expert testimony, including the possibility of a Frye hearing.

## Legal Principles

- Expert testimony on eyewitness identification is not categorically inadmissible; it may be admitted when it assists the factfinder under the rules governing expert evidence.
- Proper expert testimony generally addresses factors that can affect eyewitness perception, memory, and recall, rather than opining on whether a particular witness is accurate or truthful.
- Trial courts act as gatekeepers and may exclude such testimony based on relevance, helpfulness, risk of confusion, or unfair prejudice.
- When requested and appropriate, a trial court may conduct Frye review to determine whether the expert’s principles and methodology have achieved general acceptance in the relevant scientific community.

## Conclusion

Pennsylvania shifted from categorical exclusion to discretionary admissibility for expert testimony on eyewitness reliability, directing trial courts to evaluate such evidence case by case and to use Frye review where warranted.


Commonwealth v. Walker, 92 A.3d 766 (Pa. 2014)