---
title: "Corrections Expert Barred From Testifying About Witness Credibility"
meta:
  "og:description": "The testimony of the corrections expert was partially excluded because it included assessments of witness credibility"
  "og:title": "Corrections Expert Barred From Testifying About Witness Credibility"
  author: "Expert Witness Profiler"
  description: "The testimony of the corrections expert was partially excluded because it included assessments of witness credibility"
---

# Corrections Expert Barred From Testifying About Witness Credibility

Posted on October 31, 2025 by Expert Witness Profiler

Plaintiff Deoz Miller-Harris, formerly a detainee at the Onondaga County Justice Center (“OCJC”) alleged that the Defendants Onondaga County (the “County”) sheriff’s office employees Dustin Saddock, Ryan Whitmore, Anthony Tineo, Thomas Fodaro, Vedad Hujdur, and James Quigley (the “Individual Defendants”) violated his civil rights by using excessive force against him on September 16, 2021, and that the County negligently supervised, trained, and retained the Individual Defendants.

Subsequently, the Defendants identified two expert witnesses they intended to call at trial: (1) retired sheriff [Gerry D. Billy](https://expertwitnessprofiler.com/expert-witness/Gerry-Billy/1568777) and (2) neurologist Dr. [Robert Knapp](https://expertwitnessprofiler.com/expert-witness/Robert-Knapp/1522851). In response, Plaintiff filed a motion _in limine_ seeking to limit the testimony of both experts.

## **Corrections Expert Witness**

[Gerry D. Billy](https://expertwitnessprofiler.com/expert-witness/Gerry-Billy/1568777) completed six full terms (24 years) as the Sheriff of Licking County, Ohio, and has been in the profession of law enforcement and corrections for over three decades.

In addition, he has authored a number of articles in national publications on jail, law enforcement and management related topics and he was also the co-author of Ohio’s Basic Correctional Officer’s Training curriculum.

Furthermore, Billy has served as a consultant to the U.S. Department of Justice, the National Institute of Corrections, the Bureau of Justice Statistics, the Bureau of Indian Affairs, and the U.S. Attorney General’s Office.

[Want to know more about the challenges Gerry Billy has faced? Get the full details with our Challenge Study report](https://expertwitnessprofiler.com/order/add?eId=1568777&amp;pId=3).

## **Neurology Expert Witness**

[Robert Knapp](https://expertwitnessprofiler.com/expert-witness/Robert-Knapp/1522851) is a neurologist Board Certified by the American Board of Psychiatry and Neurology. He received his medical degree from the University of Pittsburgh School of Medicine in 1982. He has been a practicing neurologist for over 40 years.

[Discover more cases with Robert Knapp as an expert witness by ordering his comprehensive Expert Witness Profile report](https://expertwitnessprofiler.com/order/add?eId=1522851&amp;pId=3).

## **Discussion by the Court**

### **a. Billy**

According to Defendants, Billy “will opine all actions of the sworn staff were commensurate with standard corrections training, procedures and practices, and were properly deployed to maintain safety and security.”

However, Plaintiff contended that Billy should not be permitted to: (1) testify to a factual narrative, which would usurp the role of the witnesses; (2) offer his opinion about the credibility of other witnesses, which would usurp the role of the jury; or (3) provide an opinion on the ultimate issue in the case, i.e., whether Defendants used excessive force.

In turn, Defendants clarified that Billy would not offer factual narratives, assess witness credibility, or provide ultimate legal conclusions. Instead, they explained that Billy’s testimony would focus on technical corrections practices beyond the understanding of laypersons, including force techniques employed by the deputies and whether such techniques conformed to professional standards.

After considering both sides, the Court ruled that Billy was precluded from testifying to a factual narrative because he lacked personal knowledge of the underlying facts. Additionally, he was barred from assessing witness credibility or drawing legal conclusions. Nonetheless, the Court denied Plaintiff’s motion to the extent that he sought to preclude Billy’s testimony “in its entirety.”

### **b. Knapp**

Plaintiff contended that Knapp should not be permitted to refer to specific instances of his past drug use, discuss post-incident psychiatric conditions such as grandiosity, depression, and mild homicidal ideations, or conflate psychiatric diagnoses with their symptoms. Conversely, Defendants argued that Knapp’s testimony about Plaintiff’s drug use was relevant to damages and alleged injuries, and his discussion of post-incident conditions would provide important context for evaluating the etiology of Plaintiff’s seizure disorder.

After review, the Court held that Knapp could not testify regarding specific instances of the Plaintiff’s past drug use, as such testimony would be highly prejudicial, only marginally probative, and likely to confuse or mislead the jury. Nevertheless, the Court allowed Knapp to testify about the Plaintiff’s post-incident diagnoses because such expert testimony might assist in rebutting or mitigating damages.

## **Held**

- The Court granted in part and denied in part the Plaintiff’s motion _in limine_ to limit the testimony of Gerry D. Billy.

- The Court granted in part and denied in part, without prejudice to renew at trial if necessary, the Plaintiff’s motion _in limine_ to limit the testimony of Robert Knapp.

## **Key Takeaway**:

When an expert intends to offer an opinion relevant to the application of a legal standard, the expert’s role is limited to describing sound professional standards and identifying departures from them.

## **Case Details:**

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