Prosecutors in Pennsylvania, when prosecuting certain sexual violence cases, have a very powerful tool at their disposal in the form of expert victim behavior witnesses. These expert witnesses allow the government to explain away or rebut erratic behaviors or behaviors that are inconsistent with how most untrained people believe a real victim would act.

Colloquially known as a "blind expert," these expert witnesses are statutorily allowed under 42 Pa.C.S. Section 5920. The statute generally provides that in certain criminal offenses (sexual offenses) the prosecutor may call an expert to help explain certain behaviors of an alleged witness. The expert may testify regarding specific types of victim responses and victim behaviors. However, the witness may not directly testify about the credibility of another witness. Commonwealth v. Beatty, 2025 PA Super 96 (2025).

The "Blind Expert" Concept

The expert is known as a "blind expert" because they are generally not permitted to review the case file at hand, talk to the alleged victim, or reach an independent determination as to the credibility of a witness/complainant. In practice, a prosecutor will call this expert witness to the stand and ask them a series of hypothetical questions.

This testimony is intended to provide context for behaviors that may appear counterintuitive to laypersons, such as delayed disclosure, recantation, or denial of abuse.

Problems with This Testimony

The statute and testimony has led to many problems and constitutional issues. The first and most obvious problem is confirmation bias in the expert. Consider the following examples:

• Complaining witness failed to report a crime for 10 years → expert testifies this is "consistent with" being a victim
• Complaining witness immediately reported the crime → expert testifies this is also "consistent with" being a victim

This "up is down, down is up" testimony is particularly troublesome at trial.

How Defense Attorneys Can Challenge These Experts

A skilled defense attorney can attack these experts in the following ways:

1. Pointing out that these expert witnesses usually serve a role of an "advocate" and not someone who critically assesses each situation
2. Just about any behavior could be consistent with a person who has been victimized
3. The expert witness likely cannot come up with any situation where an alleged victim's behavior would be inconsistent with a person who has actually been sexually victimized
4. These expert witnesses are paid by the Commonwealth to testify, and are usually retained on more than one case
5. The expert usually has worked for the Commonwealth for many years and has interacted primarily with alleged victims, detectives, police, and prosecutors
6. These witnesses rarely, if ever, testify on behalf of a defendant or even work with defense attorneys