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United States v. Cerna, 2010 WL 3448528 (N.D. Cal. 2010)

Case (cite)
United States v. Cerna, 2010 WL 3448528 (N.D. Cal. 2010)
Type of proceeding
Type of claim
Type of claim (second claim)
Expert evidence ruling reversing or affirming on appeal:
What was the ruling?
Type of evidence at issue:
Firearms identification
Defense or Prosecution Expert
Name of expert(s) who were the subject of the ruling
John Sanchez, Mark Proia, G. Andrew Smith
Summary of reasons for ruling
Defendants argue the expert testimony should be excluded because the AFTE theory used by the experts is unreliable and because the government's expert disclosures were "so inadequate defendants cannot make fact-specific challenges to the experts' specific application of the AFTE theory . . . ." The court held the AFTE theory is sufficiently reliable under both Daubert and 702. The court cites to precedent (Diaz) and explains that nothing has changed since that decision to cast doubt on the reliability of the AFTE theory to exclude it. The court disagrees with defense counsel's arguement that the NAS2009 report is enough to exclude any expert testimony using the AFTE theory and states that the report speaks to the individual expert's application of the theory rather than the thoeyr itself. The other issues raised by the NAS2009 report were addressed in Diaz. Further, the court holds that the limitations in Glynn are not persuasive because limiting an expert to testifying "more likely than not" indicates that they are no more than 51% sure there was a match, and that the "practical certainty" is not preferable to the Diaz "reasonable degree of certainty in the ballistics field" standard. Finally, the court finds that the reliability of the AFTE standard does not depend on the gun being recovered. The court holds that no pretrial hearing is necessary, but that the prosecution must prove that the AFTE theory passes Daubert for the testimony to be considered by the jury.
The jurisdiction’s standard for expert admissibility at the time – list all that apply: (Frye), (Daubert), (Post-2000 Rule 702), (Other)
Second standard
Rule 702
Did lower court hold a hearing
Names of prosecution expert(s) two testified at hearing
Names of defense expert(s) who testified at hearing (or None).
Discussion of 2009 NAS Report (NAS2009)
Discussion of 2016 PCAST report (PCAST)
Discussion of error rates / reliability
Frye Ruling
Limiting testimony ruling
Language imposed by court to limit testimony
Ruling based in prior precedent / judicial notice
Daubert ruling emphasizing – which factors – (list 1-5)
Ruling on qualifications of expert
Ruling on 702(a) – the expert will help / assist the jury
Ruling on 702(b) – the testimony is based on sufficient facts or data
Ruling on 702(c) – the testimony is the product of reliable principles and methods
Ruling on 702(d) – reliable application of principles and methods to the facts of the case


A 2009 report from the National Research Council of the National Academy of Sciences highlights weaknesses in the AFTE theory. . . . These weaknesses, however, do not require the automatic exclusion of any expert testimony based on the AFTE theory. The weaknesses highlighted by the NAS report—subjectivity in a firearm examiner’s identification of a “match” and the absence of a precise protocol—are concerns that speak more to an individual expert’s specific procedures or application of the AFTE theory, rather than the universal reliability of the theory itself. Indeed, the NAS report notes that although the “process for toolmark and firearms comparisons lacks the specificity of the protocols for, say, 13 STR DNA analysis … [t]his is not to say that toolmark analysis needs to be as objective as DNA analysis in order to provide value” (id. at 155). Moreover, the general issues raised in the NAS report were grappled with in the Diaz order—the order addressed criticism that the AFTE theory involves subjectivity, the standards controlling the analysis of firearms identification can be construed as vague, and there is no single, precise error rate.




Notably, the co-chair of the committee that issued the NAS report, Judge Harry T. Edwards, has specifically noted that the NAS report is not a law reform proposal and that “whether forensic evidence in a particular case is admissible under applicable law is not coterminous with the question whether there are studies confirming the scientific validity and reliability of a forensic science discipline.” . . . . True, the NAS report has been cited by the Supreme Court. . . . The NAS report was cited, however, for the proposition that forensic evidence in general is manipulable (ibid.). This does not undermine the proposition that the AFTE theory is sufficiently reliable to at least be presented to a jury, subject to cross-examination. Accordingly, the NAS report does not necessitate exclusion of expert testimony simply because an expert employed the AFTE theory. Instead, the NAS report may be used for cross-examination or may offer guidance for fact-specific challenges. The AFTE theory need not be perfect science to satisfy Daubert so long as it is sufficiently reliable


No pretrial evidentiary hearing regarding the AFTE theory in general is needed at this time. Yes, the trial court serves as a gatekeeper, but this gatekeeping role is “not intended to serve as a replacement for the adversary system.” Fed.R.Evid. 702, Advisory Committee’s Note. Instead, “[v]igorous cross-examination, presentation of contrary evidence, and careful instruction on the burden of proof are the traditional and appropriate means of attacking shaky but admissible evidence.” Daubert, 509 U.S. at 595 (citation omitted). Of course, there is a benefit for counsel to have a “free shot” at the firearms experts prior to their testimony before the jury. Nonetheless, this is not the normal procedure used in criminal cases. Cross-examinations in criminal cases are almost always cold-cross examinations.