People v. Azcona, 272 Cal.Rptr.3d 471 (Ct. App. Cal. 2020)

The expert’s explanation of his conclusions: “He explained: “I need to see six individual marks in a row [ ] to meet my identification criteria. That’s based on the fact that nobody’s ever seen that many by random chance. [¶] We’ve done numerous studies on the subject trying to see what can happen by random chance, and that’s much more than can ever happen by random chance. [¶] So if you see these marks and all your class characteristics are the same and you can identify the source of the marks, it is possible to say they were fired from the same gun. And the thing that’s good to add on now days is not just that they were fired from the same gun, but to the practical exclusion of all other guns.””

“Expert testimony based on the application of a scientific technique is admissible in California if the technique is generally accepted in the pertinent scientific community. . . . That test has been criticized as essentially delegating admissibility to scientists without a judge directly confronting the reliability of the evidence. . . . But the Supreme Court has continued to endorse the Kelly standard, reasoning that “it may be preferable to let admissibility questions regarding new scientific techniques be settled by those persons most qualified to assess their validity.” ”

On using Kelly (Frye) over Daubert: “The California approach is a departure from the test applied to novel scientific evidence in federal courts. Rather than admitting the evidence based on a general consensus about its reliability, federal courts, under Daubert v. Merrell Dow Pharm., Inc. (1993) 509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469, conduct a broader inquiry which allows the court to exercise its own judgment about whether the technique used is reliable. . . . In contrast, “[u]nder the Kelly test, the admissibility of evidence obtained by use of a scientific technique does not depend upon proof to the satisfaction of a court that the technique is scientifically reliable or valid. Because courts are ill suited to make such determinations, admissibility depends upon whether the technique is generally accepted as reliable in the relevant scientific community.” . . . As a result of the difference in state versus federal approaches, the federal authorities cited by defendant are of limited value here because they focus on directly examining the reliability of toolmark comparison methods”

Defendant presented legitimate criticism from credible sources: scientific reports commissioned by the federal government, and testimony by a research scientist. That evidence undermines the reliability of the method and casts some doubt on the prosecution expert’s conclusion that particular bullet casings came from the same firearm. The information was therefore relevant and important for the jury to consider in assessing the expert testimony. And the jury was afforded that opportunity through defense counsel’s extensive cross-examination of the prosecution expert regarding those very criticisms of the method. The expert acknowledged he was aware of the reports but disagreed with them, and thought the authors were not qualified to conduct firearms analysis. Criticism of the method from credible sources surely affects the persuasive value of the evidence, but it does not equate to what defendant needed to show to render the firearms expert’s testimony inadmissible: that the method is no longer accepted by a clear majority of the relevant scientific community.