United States v. Cazares, 788 F.3d 956 (9th Cir. 2015)

Even the government is not arguing on appeal that “scientific certainty” is a proper characterization for toolmark identification expert testimony. While there may be some deficiency in the objections to the standard testified to by Paul, it appears that the “scientific certainty” issue was brought to the district court’s attention before and during Paul’s testimony. A more thorough Daubert hearing could have been helpful in handling the “scientific certainty” issue. The issue is then whether the “scientific certainty” characterization was harmless error.
48 An error is harmless unless it results in actual prejudice, which is demonstrated where “the error in question had a ‘substantial and injurious effect or influence in determining the jury’s verdict.’ ” Winzer, 494 F.3d at 1201 (quoting Brecht, 507 U.S. at 623, 113 S.Ct. 1710). Although the firearms identification evidence and expert testimony was important in this case, the “scientific certainty” characterization was subject to cross examination which resulted in acknowledgment of subjectivity in the expert’s work. In addition, the district court properly instructed as to the role of expert testimony and there was substantial evidence otherwise linking the defendants to the Wilson and Bowser murders. We believe “a reasonable degree of certainty in the ballistics field” is the proper expert characterization of toolmark identification. Any error in this case from the “scientific certainty” characterization was harmless.