Brief for John Monahan, David Faigman, Christopher Slobogin, Edward Imwinkelried, Jennifer Mnookin, Roger Park, Paul Rothstein, and 15 other Evidence Professors as Amici Curiae Supporting Respondent (Diaz v. United States, Supreme Court No. 23-14)

Amici are twenty-two current and emeritus law professors who teach and research Evidence law. Some of us authored the most frequently cited textbooks and treatises. Among us are former prosecutors and de- fense attorneys. Three of us are recipients of the John Henry Wigmore Lifetime Achievement Award for Evidence scholarship. A complete list of amici can be found in the Appendix. Amici have no personal interest in this case and write solely to inform the Court on how we think Rule 704(b) ought to be interpreted, considering evidence doctrine and practice.<br><br>SUMMARY OF ARGUMENT <br><br>When experts provide opinions about how most drug traffickers behave and what most drug traffickers know, they are not drawing and cannot draw conclusive inferences about whether an individual possessed the requisite mens rea. Instead, they are providing “framework” evidence—evidence that bears on the likelihood of a fact being true, based on the defendant’s membership in a particular group. The jury still decides whether to believe the expert’s framework testimony, how much weight to give it, and separately, whether the group data apply to the facts of this case. For these reasons, experts who testify under Rule 704 as to how members of a group tend to think do not replace the jury’s ultimate fact-finding regarding mens rea. <br><br>Experts who provide reliable framework evidence merely provide an opinion about general facts in the world. So long as they do not opine on an individual defendant’s mental state, this does not run afoul of Federal Rule of Evidence 704(b). The Court should not adopt the Petitioner’s interpretation of Rule 704(b), because an expert’s framework testimony is not the “functional equivalent” of telling the jury how to decide the case. United States v. Gutierrez-Farias, 294 F.3d 657, 663 (5th Cir. 2002). Petitioner’s view conflates several separate inferences, and thus violates norms of evidence doctrine that treat each inference independently. Additionally, Petitioner’s interpretation 1) relies on an inaccurate view of mental states and how they are inferred, 2) assumes that jurors are incapable of drawing individual inferences and assessing the credibility and weight of mental state expert testimony, and that attorneys are incapable of exposing any weaknesses on cross-examination, 3) denies jurors access to a critical source of expert framework evidence, and 4) triggers interpretive inconsistencies and thus more appellate litigation. <br><br>The Court can answer the Question Presented and improve the functionality of Rule 704(b) by drawing a clearer line between an expert’s permitted group testimony and the jury’s application of that group testimony to a particular defendant. Fears that 704(b) testimony might become the “functional equivalent” of telling the jury how to decide the case can be laid to rest by having judges explain to the jury in plain terms the group nature of the expert’s testimony and its independence from the jury’s factual determination. There is nothing unique about Rule 704(b) testimony that warrants blocking the jury from assessing its credibility. The rule specifically reminds us that determinations of a defendant’s mental state or condition are “matters [] for the trier of fact alone.” FED. R. EVID. 704(b). If the foundation and purpose of the expert’s framework testimony is made clear, such testimony can be relevant and useful, and thus ought to be admissible. Denying jurors access to probative framework evidence would be ill-advised in the many cases where lay jurors’ intuitions are at odds with experts’ specialized knowledge, which may unduly prejudice criminal defendants.