Wesley Cotton alleged that on March 19, 2022, an incident occurred on Yard 3C at California State Prison, Corcoran (“CSP-Corcoran”), in which officers deployed multiple chemical agents, including oleoresin capsicum (“OC”), chloroacetophenone (“CN”), chlorobenzalmalononitrile (“CS”) grenades (collectively, “chemical agents”) to stop a fight between third party prisoners.
At the time the chemical agents were deployed, Cotton was located on an adjacent yard, 3B. Cotton alleged that Defendant Medina failed to protect him from exposure to the chemical agents which travelled from Yard 3C into Yard 3B, where he was locked in a caged enclosure. The alleged exposure caused Cotton to choke and injured his eyes, lungs, and body.
Cotton challenged the testimony of Defendant’s expert witness, Sgt. M. Contreras, an armory sergeant at CSP-Corcoran, on multiple grounds.
Law Enforcement Expert Witness
M. Contreras is a veteran law enforcement officer with nearly twenty-five years of experience and has worked as an armory sergeant at CSP-Corcoran since 2017 where he became familiar with the facilities and layout of Yards 3B and 3C.
Over the course of his career, Contreras developed extensive and specialized knowledge regarding the maintenance, handling, and use of chemical agents and use-of-force munitions including OC, CN, and CS gas grenades.
Discussion by the Court
a. Objection to Defendant’s Rule 26 Disclosures
Cotton moved to exclude the testimony of M. Contreras under FRCP 26(a)(2) and 37(c)(1), alleging that Defendant is trying to “sneak in” M. Contreras as a new witness outside of the discovery timeline and without proper notice.
To begin with, Cotton claimed that Defendant failed to disclose Contreras in the initial or final witness lists (May 11, 2023), the non-expert deadline (January 19, 2024), or the expert deadline (February 23, 2024) and that Defendant failed to show substantial justification or lack of harmlessness for the late disclosure or harmlessness.
The Court noted multiple deficiencies in Cotton’s argument, mainly that according to the “Second Scheduling Order” in this case, the deadline for all parties to serve their expert disclosures was August 15, 2025.
Defendant provided evidence that she did in fact timely disclose and serve on Cotton the Rule 26 expert report for M. Contreras on August 15, 2025, more than 90 days before the January 27, 2026 scheduled trial date.
b. Motion to Strike
i. Daubert Admissibility
Contreras relied on “his experience and training on the nature, use, and effective range of the specific chemical munitions deployed in the underlying incident” in formulating his opinion that an individual located on CSP-Corcoran’s 3B Yard – located approximately 750 feet south of where chemical agents were deployed on CSP-Corcoran’s 3C Yard during the March 19, 2022 incident and separated by multiple buildings – would not have been affected by the chemical agents. Furthermore, in reaching his opinion, Contreras reviewed reports from the March 19, 2022 incident, surveillance-camera and body-worn camera footage of the incident and conducted a physical inspection and measured the incident location.
In a motion related to Contreras’ testimony, Cotton claimed that “as only an armory officer/sergeant, Contreras presents no accredited training in CN chemical composition, gas dispersion or meteorology – yet seeks to offer scientific-type opinions.” However, Cotton does not elaborate on Contreras’ alleged lack of qualifications, lack of personal knowledge, or his accusation that allowing M. Contreras to testify would constitute “unfair prejudice/confusion/waste given CCPOA allegiance and armory-only role.”
As a result, the Court is satisfied that Contreras’ “specialized knowledge and experience can serve as the requisite ‘facts or data’ on which [he may] render an opinion.” Contreras has provided the “how and why” underlying his conclusions and opinion in this case, which appears to be, at least in part, his knowledge and expertise with the CSP Corcoran premises and the nature, use, and effective range of the specific chemical munitions at issue in this caser to arrive at his conclusion. The Court also found that there is no evidence of Contreras showing improper “allegiance” to either Defendant or CSP-Corcoran.
ii. Exclusion under Rules of Evidence 602, 802, 701(c), and 403
Cotton complained that Contreras’ testimony and expert report failed to satisfy the criteria of the various Federal Rules of Evidence.
As a threshold matter, because Defendant intended to have Contreras testify as an expert witness, Cotton’s invocation of Federal Rules of Evidence 602 and 701(c) as grounds for exclusion are unavailing.
Cotton’s invocation of Rule 802 and 403 was similarly unpersuasive. Out-of-court statements are inadmissible hearsay when they are offered to prove the truth of the matter asserted.
Cotton did not explain how Contreras’ testimony or expert report constitutes inadmissible hearsay, as Contreras’ opinion appeared to be based on non-hearsay evidence, including his professional training, operational experience, physical inspection and measurement of the incident locations, and review of surveillance and body-warn-camera footage of the incident.
Held
The Court denied Cotton’s motions to strike the testimony of Defendant’s expert witness, M. Contreras.
Key Takeaway
An expert need not rule out every potential cause in order to satisfy Daubert, as long as the expert’s testimony addresses obvious alternative causes and provides a reasonable explanation for dismissing specific alternate factors identified by the defendant.
Case Details:
| Case Caption: | Cotton V. Medina |
| Docket Number: | United States District Court for the Eastern District of California |
| Court Name: | 1:22cv568 |
| Order Date: | January 19, 2026 |
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