Flexible Daubert Gatekeeping and Circumstantial Proof of “Death Results” under § 841: United States v. Jackasal (11th Cir. 2025)

Flexible Daubert Gatekeeping and Circumstantial Proof of “Death Results” under § 841: United States v. Jackasal (11th Cir. 2025)

Court: U.S. Court of Appeals for the Eleventh Circuit (Non-Argument Calendar; unpublished)

Panel: Judges Jill Pryor, Newsom, and Brasher (per curiam)

Date: September 2, 2025

Docket No.: 24-11011

Introduction

This appeal arises from the conviction of Kavon Jackasal for distributing fentanyl that resulted in the death of Valerie Mouw, triggering the “death results” penalty enhancement under 21 U.S.C. § 841(b)(1)(C). Two core issues were presented: (1) whether the district court abused its discretion under Federal Rule of Evidence 702 and Daubert by admitting a Drug Enforcement Administration forensic chemist’s expert testimony identifying fentanyl via gas chromatography–mass spectrometry (GC-MS); and (2) whether the trial evidence was sufficient to prove beyond a reasonable doubt that the fentanyl distributed by Jackasal was the but-for cause of Mouw’s death, as required by the Supreme Court’s decision in Burrage v. United States.

The Eleventh Circuit affirmed on both issues. The panel emphasized the flexible nature of Daubert’s reliability inquiry and endorsed the district court’s reliance on general acceptance and peer-reviewed support for GC-MS as sufficient to admit the chemist’s testimony—even in a jury trial. On causation, the court held that the circumstantial and expert evidence permitted a reasonable jury to find beyond a reasonable doubt that Mouw’s death resulted from fentanyl supplied by Jackasal.

Summary of the Judgment

  • Daubert/Rule 702: No abuse of discretion in admitting the DEA chemist’s GC-MS testimony. The district court reasonably relied on the methodology’s general acceptance in the scientific community and peer-reviewed literature describing GC-MS as a “gold standard,” and properly exercised flexibility in deeming some Daubert factors inapt for the test at issue.
  • Sufficiency of the Evidence (Death-Results Enhancement): The evidence—including text messages, the pattern of prior fentanyl transactions, a controlled follow-up in which the officer asked for the “same product,” and expert toxicology/medical examiner testimony—allowed a reasonable jury to find that fentanyl from Jackasal was the but-for cause of Mouw’s death.
  • Disposition: Conviction affirmed.

Analysis

Precedents Cited and Their Influence

  • Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993): Established four non-exhaustive reliability factors for expert testimony: testability, peer review/publication, error rate/standards, and general acceptance. The panel reiterated that this inquiry is “flexible” and not a rigid checklist.
  • Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999): Confirmed that Daubert’s reliability inquiry applies to all expert testimony (scientific, technical, or specialized) and that district courts have broad latitude in both how to assess reliability and in their ultimate reliability determinations. This undergirded the district court’s decision to downplay inapt factors such as “falsifiability” for this GC-MS application.
  • United States v. Brown, 415 F.3d 1257 (11th Cir. 2005): Emphasized deference to district courts on Daubert issues and held that, “in the right circumstances,” expert evidence may be admissible even if three of the four Daubert factors are not satisfied. The defense argued Brown should be limited because it involved a bench trial, but the panel rejected a rigid bench/jury distinction and reaffirmed Daubert’s flexibility.
  • United States v. Barton, 909 F.3d 1323 (11th Cir. 2018): Restated the abuse-of-discretion standard governing admissibility of expert testimony. The panel hewed closely to that deferential framework.
  • United States v. Copeland, 20 F.3d 412 (11th Cir. 1994): Noted that assessment of witness credibility is for the factfinder. The panel used this to dismiss arguments attacking the chemist’s credibility.
  • United States v. Clay, 832 F.3d 1259 (11th Cir. 2016); United States v. Williams, 865 F.3d 1328 (11th Cir. 2017); United States v. Beach, 80 F.4th 1245 (11th Cir. 2023): Articulated sufficiency-of-the-evidence principles: a verdict must stand if any reasonable construction of the evidence supports it; reversal is warranted only if no reasonable trier could find guilt; and the jury may choose among reasonable interpretations and need not exclude every hypothesis of innocence.
  • Burrage v. United States, 571 U.S. 204 (2014): Requires but-for causation to trigger § 841(b)(1)(C)’s “death results” enhancement and holds that the enhancement is an element for the jury to decide beyond a reasonable doubt. The panel applied Burrage to uphold the jury’s finding that fentanyl was the but-for cause of death.
  • United States v. Ifediba, 46 F.4th 1225 (11th Cir. 2022), and United States v. Joseph, 709 F.3d 1082 (11th Cir. 2013): Address standards of review for sufficiency claims, including plain-error review when a defendant fails to preserve. The court noted a dispute over preservation but resolved the case under the more defendant-friendly de novo standard, rendering the dispute academic.

Legal Reasoning

1) Rule 702/Daubert and the GC-MS Testimony

The court framed the admissibility question under the abuse-of-discretion standard and stressed the particularly deferential posture for Daubert decisions. The DEA chemist (Vasquez) described in detail how the lab used GC-MS to identify substances by comparing test results with the DEA’s internal library of standard reference chemicals. He explained that:

  • GC-MS is a widely used and accepted technique in forensic chemistry;
  • The DEA’s reference library was built from accredited sources and validated through DEA-run checks; and
  • Peer-reviewed literature recognizes GC-MS as a “gold standard.”

In admitting the testimony, the district court recognized that not every Daubert factor fits every method. Specifically, it concluded that “falsifiability” (testability) was not a particularly useful lens for evaluating GC-MS library matching in this forensic context. The court instead relied on general acceptance and peer-reviewed support, finding those factors compelling for GC-MS. The Eleventh Circuit approved this tailoring, citing Kumho Tire’s direction that reliability inquiries are flexible and context-dependent.

The defense’s key objection—that the district court impermissibly ran a “one-factor” (general acceptance only) analysis—was rejected. The panel highlighted that the district court also found support in peer-reviewed literature portraying GC-MS as a gold standard. The defense’s push to scrutinize the exact “level of generality” (DEA’s particular application vs. GC-MS generally) was declined; the court refused to “nit-pick” where the broader literature reliably supported the method’s core validity.

Critically, the panel concluded there was no abdication of gatekeeping—especially salient because the testimony was presented to a jury—since the district court articulated its reasoning, found the method reliable, and addressed the fit of specific Daubert factors.

2) Sufficiency of the Evidence on “Death Results” under § 841(b)(1)(C)

On sufficiency, the panel summarized a coherent evidentiary chain supporting the jury’s finding that Mouw’s death resulted from fentanyl supplied by Jackasal:

  • Text messages showed a prior trading relationship in which Mouw asked for fentanyl in exchange for crack cocaine;
  • On the night of her death, Mouw arranged a delivery from Jackasal; it was reasonable to infer the same product (fentanyl) was intended, consistent with past dealings and police testimony;
  • The next day, when an officer posed as Mouw and asked for the “same product,” Jackasal delivered fentanyl;
  • Although the fentanyl recovered in Mouw’s room appeared to be from a different batch than that seized later from Jackasal’s car, police testified that street-level dealers commonly source the same drug from different batches or suppliers, blunting any inference that batch differences undermine the distribution link;
  • The toxicologist testified the fentanyl concentration was sufficient to cause overdose and that Mouw’s body position was typical for fentanyl overdoses;
  • The medical examiner opined that fentanyl, not gabapentin or other substances, caused death: the fentanyl level would be “therapeutic” only with respiratory support (which she lacked), there was no evidence of gabapentin toxicity (e.g., hypertension), and no gabapentin pill fragments were found.

Under Burrage’s but-for standard, this evidence allowed a reasonable jury to conclude beyond a reasonable doubt that fentanyl supplied by Jackasal caused Mouw’s death. The court emphasized that circumstantial evidence can suffice; the jury may choose among reasonable interpretations and need not eliminate every alternative hypothesis (such as the defense’s gabapentin theory).

Impact and Practical Implications

A. Rule 702 Gatekeeping in Drug Identification Cases

  • Flexibility Endorsed: The decision reaffirms district courts’ leeway to tailor Daubert factors to the method at issue. Where a technique like GC-MS enjoys deep, peer-reviewed acceptance in the relevant scientific community, general acceptance plus literature support may suffice—even without granular proof of some factors (e.g., specific error rates or method “falsifiability”) in every case.
  • Jury vs. Bench Trials: Although Brown noted less stringent gatekeeping concerns in bench trials, Jackasal clarifies that the flexible approach remains available in jury trials, provided the court adequately explains its reliability findings and does not abdicate its gatekeeping role.
  • Level of Generality: Courts can rely on the widely accepted scientific foundation of a method (e.g., GC-MS) without demanding peer-reviewed publications specific to one lab’s internal application, so long as the core technique is validated and responsibly implemented.
  • Laboratory Practices: The DEA’s use of accredited reference materials and internal validation bolstered reliability. Forensic labs should ensure record evidence of such practices is clearly presented to withstand Daubert challenges.

B. “Death Results” under § 841(b)(1)(C)

  • Circumstantial Proof Recognized: The court endorsed a pragmatic approach to proving but-for causation through a combination of communications, sales patterns, controlled buys, and medical evidence. Exact batch matching was not required.
  • Alternative Cause Theories: Defense theories pointing to other substances (e.g., gabapentin) will falter if medical evidence persuasively explains why the alternative is inconsistent with observed physiology or autopsy findings.
  • Burrage in Practice: Burrage’s but-for requirement does not demand direct scientific sameness between samples if the circumstantial chain firmly supports that the defendant’s drug use was the sine qua non of death.

C. Standards of Review and Preservation

  • Deference Matters: Appellate courts are reluctant to second-guess district court Daubert rulings; a carefully reasoned gatekeeping order will usually stand.
  • Preservation: The panel sidestepped a dispute over whether sufficiency was preserved by noting the conviction stood even under de novo review. Practitioners should still preserve Rule 29 motions to avoid plain-error constraints on appeal.

D. Relationship to the 2023 Rule 702 Amendments (Context)

Although not discussed in the opinion, the 2023 amendments to Rule 702, emphasizing the trial court’s gatekeeping duty and the proponent’s “more likely than not” burden on each Rule 702 element, are consistent with this ruling’s approach. Jackasal illustrates that a robust record on general acceptance and peer-reviewed support can carry the proponent’s burden, even if not every Daubert factor is squarely applicable to the specific methodology.

Complex Concepts Simplified

  • Daubert Factors: Courts look at indicators of reliability like whether an expert’s method can be tested, is peer-reviewed, has known error rates and standards, and is generally accepted. Not every factor must apply in every case; the inquiry is flexible.
  • GC-MS (Gas Chromatography–Mass Spectrometry): A forensic method that separates components of a substance (gas chromatography) and identifies them by their mass and charge (mass spectrometry), often by matching to a library of known reference spectra. It is widely used to identify drugs.
  • Rule 702 Gatekeeping: Judges act as “gatekeepers” to ensure expert testimony is relevant and reliable before the jury hears it. The proponent must show reliability by a preponderance of the evidence.
  • “Death Results” Enhancement (21 U.S.C. § 841(b)(1)(C)): In drug distribution cases, if death or serious bodily injury “results from” use of the drug distributed, the statute imposes a heightened sentencing range. The Supreme Court in Burrage requires proof that the drug was a but-for cause of death.
  • But-For Causation: The “sine qua non” test: the death would not have happened when it did but for use of the defendant’s drug. Other contributing factors can exist; the government must show the drug’s use was a necessary condition of death.
  • Sufficiency of the Evidence Standard: On appeal, the court asks whether any reasonable jury could have found guilt beyond a reasonable doubt based on the evidence. The jury may choose among reasonable interpretations and does not have to eliminate every speculative alternative.
  • Plain Error vs. De Novo (Preservation): If a defendant fails to preserve a challenge (e.g., a Rule 29 motion for acquittal), the appellate court reviews only for “plain error,” which is harder to meet. Properly preserved challenges receive de novo review.

Practice Pointers

  • For the Proponent of Expert Evidence:
    • Build a record on general acceptance and peer-reviewed support for the method (e.g., GC-MS);
    • Document accreditation of reference libraries and internal validation/quality control steps;
    • Explain why certain Daubert factors (e.g., testability in a Popperian sense) may be inapt for the method and how reliability is instead ensured;
    • Connect the method’s reliability to the specific casework procedures used in the lab.
  • For the Opponent (Challenging Reliability):
    • Probe the lab’s application-specific practices (calibration, controls, contamination safeguards, error rates, and library curation);
    • Distinguish general acceptance of the technique from the particular lab’s implementation, if there are weaknesses;
    • Offer alternative scientific literature and expert testimony, where possible, to challenge “gold standard” assertions.
  • On “Death Results” Proof:
    • Prosecutors can rely on robust circumstantial evidence of distribution and use, plus medical testimony linking the drug to the mechanism of death;
    • Defense counsel should develop credible alternative-cause theories supported by medical/scientific evidence, and cross-examine on pharmacology, symptomatology, and autopsy findings;
    • Both sides should anticipate arguments about batch/source variability and address them with street-level distribution realities or forensic traceability, respectively.
  • Preservation: Always renew Rule 29 motions and specify grounds to safeguard appellate review under the most favorable standard.

Conclusion

United States v. Jackasal reaffirms two enduring principles. First, Daubert’s reliability inquiry is flexible. A district court does not err by emphasizing general acceptance and peer-reviewed support where those factors credibly establish the reliability of a forensic method like GC-MS, even in a jury trial and even when other Daubert factors are less illuminating for the method at issue. Second, under Burrage, but-for causation for the § 841(b)(1)(C) “death results” enhancement can be proven through a cohesive blend of circumstantial proof and medical testimony; exact batch-matching is not indispensable when the evidentiary mosaic convincingly points to the defendant’s drug as the necessary cause of death.

While unpublished and therefore non-binding, the decision is instructive in narcotics prosecutions and forensic evidence litigation in the Eleventh Circuit. It underscores the importance of a well-developed reliability record for laboratory methods and confirms that juries may reasonably infer causation from circumstantial and expert evidence in complex overdose cases. The key takeaway is pragmatic: courts will credit widely accepted, literature-supported forensic techniques and coherent causal narratives that fit the medical evidence. Practitioners should shape their Daubert strategies and causation proofs accordingly.

Case Details

Year: 2025
Court: Court of Appeals for the Eleventh Circuit

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