## Facts

- Chaz Glynn was charged with murder in aid of racketeering, murder in connection with drug trafficking, and murder through use of a firearm under federal statutes.
- A first jury trial ended in a mistrial after the jury reported it was hopelessly deadlocked; the court set the case for retrial.
- The government sought to offer NYPD firearms examiner Detective James Valenti as an expert in firearms/toolmark identification.
- Valenti proposed to opine, “to a reasonable degree of ballistic certainty,” that a bullet recovered from the victim and shell casings from related scenes were fired from firearms associated with Glynn.
- Glynn moved under Federal Rule of Evidence 702 to exclude the testimony as insufficiently reliable under Daubert and Kumho.
- After a Daubert/Kumho hearing, the court reaffirmed its prior trial ruling admitting the evidence but restricting the form and strength of the expert’s conclusions, with a minor modification for retrial.

## Issues

1. Whether firearms/toolmark identification testimony satisfies Rule 702 reliability requirements under Daubert and Kumho such that it may be admitted.
2. Whether a firearms examiner may describe the discipline as a “science” or express identification conclusions in terms of “certainty,” including “a reasonable degree of ballistic certainty.”
3. What level of conclusory strength is permissible to reduce the risk of misleading the jury about the method’s reliability and precision.

## Decision

- The court denied the motion to exclude firearms/toolmark testimony in full, finding the methodology had sufficient support to meet the threshold for admissibility under Rule 702.
- The court granted the motion in part by limiting how the expert could express his conclusions.
- The expert was prohibited from testifying that firearms identification is a “science” or that any identification was reached to any degree of “certainty,” including “a reasonable degree of ballistic certainty.”
- The expert was limited to a probabilistic formulation, permitted to testify only that it was “more likely than not” that the bullet and casings came from the firearms linked to Glynn.

## Legal Principles

- Under Rule 702 and Daubert/Kumho, courts must act as gatekeepers to ensure expert testimony is based on sufficient facts or data and reliable methods, and is reliably applied to the case.
- Firearms/toolmark identification may be admissible even where the comparison process depends substantially on examiner judgment and lacks objective, well-defined standards for declaring a “match.”
- Where a field lacks validated, well-quantified error rates and employs qualitative criteria (e.g., “sufficient agreement”), an examiner may be restricted from using language that implies scientific precision or near-absolute certainty.
- Expert phrasing that conveys “certainty” risks misleading jurors, particularly in criminal cases, by suggesting the evidence carries a level of accuracy comparable to the beyond-a-reasonable-doubt standard.
- Trial courts may admit firearms identification testimony while limiting conclusions to modest probabilistic statements (e.g., “more likely than not”) to prevent overstatement and preserve the jury’s role in assessing guilt.

## Conclusion

The court held that firearms/toolmark comparison evidence could be presented under Rule 702, but only in a substantially qualified form: the examiner could not claim scientific certainty and could opine only that a match was “more likely than not,” to reduce the risk of juror confusion and overstatement of the method’s reliability.


United States v. Glynn, 578 F. Supp. 2d 567 (S.D.N.Y. 2008)