Limitations on Expert Testimony Under Federal Rule of Evidence 704(b) in 18 U.S.C. § 2422(b) Enticement Cases

Introduction

United States v. Joshua Herrera is a published Eleventh Circuit decision addressing the admissibility of expert psychiatric testimony under Federal Rule of Evidence 704(b) in a federal child‐enticement prosecution. Defendant–Appellant Joshua Herrera was convicted of attempting to entice a minor to engage in sexual activity, in violation of 18 U.S.C. § 2422(b), after engaging in an extensive online exchange with an undercover FBI agent posing as a mother seeking sexual activity with her eleven‐year‐old daughter. Herrara’s defense sought to introduce psychologist testimony that he lacked any sexual interest in minors. The district court excluded that specific opinion as violative of Rule 704(b) and, in the alternative, Rule 403. On appeal, Herrera challenged the exclusion as an abuse of discretion and a constitutional violation of his right to present a defense. The Eleventh Circuit affirmed, relying principally on its prior decision in United States v. Gillis (938 F.3d 1181 (11th Cir. 2019)), which barred nearly identical testimony in a similar § 2422(b) prosecution.

Summary of the Judgment

The Eleventh Circuit issued a per curiam opinion on January 7, 2025, affirming Herrera’s conviction. The panel held:

The district court did not abuse its discretion in excluding expert testimony that Herrera’s “psychosexual assessment showed no indications that he has a sexual interest in children,” because such testimony would state an opinion on an element of the charged offense—namely, the required mental state of “knowingly” enticing a minor—contrary to Rule 704(b).
Herrera’s constitutional right to present a defense was not violated, as the exclusion was a correct application of the Federal Rules of Evidence and no “compelling reason” existed to override them.
Other challenges—including the exclusion of certain lay testimony regarding grooming and the application of Rule 403—were unnecessary to resolve because exclusion of the expert opinion alone warranted affirmance.

Analysis

Precedents Cited

United States v. Gillis (938 F.3d 1181 (11th Cir. 2019)): Held that expert testimony based on a psychosexual evaluation, stating the defendant lacked sexual interest in children, violates Rule 704(b) in a § 2422(b) enticement prosecution. This case is binding Eleventh Circuit precedent and controls Herrera’s case.
United States v. Stahlman (934 F.3d 1199 (11th Cir. 2019)): Rejected a challenge to exclusion of expert testimony that the defendant intended only to act out a fantasy rather than engage sexually with a minor. Although Stahlman discussed D.C. Circuit authorities, its remarks on Hite were dicta and not binding.
United States v. Hite (769 F.3d 1154 (D.C. Cir. 2014)): Permitted expert testimony that the defendant had no psychiatric condition associated with sexual attraction to children. Distinguished by the Eleventh Circuit as not squarely on point, and thus not controlling.
Rule 704(b) and its legislative history: Adopted in response to the Hinckley trial, Rule 704(b) prohibits expert witnesses in criminal cases from stating an opinion on whether a defendant had the mental state or condition that constitutes an element of the crime charged. The rule preserves the jury’s role on those “ultimate issues.”
Diaz v. United States (602 U.S. 526 (2024)): Clarified that an expert may opine about mental states of “most people” in a group without violating Rule 704(b) because the rule bars only opinions “about the defendant” on an ultimate issue. Diaz did not disturb Gillis’s holding as applied to § 2422(b) prosecutions.

Legal Reasoning

The court’s reasoning unfolded in two parts:

Scope of Rule 704(b): Rule 704(b) forbids expert testimony that directly addresses whether the defendant possessed the mens rea required for conviction (e.g., knowingly, intent, recklessness). The rule was enacted to rein in expert influence on juries regarding ultimate issues after the Hinckley insanity acquittal.
Application to Herrera: Herrera’s proposed opinion—that his psychosexual assessment showed no sexual interest in minors—would necessarily resolve the critical mens rea element in his favor: that he did not “knowingly entice” a minor. Drawing on Gillis, the court found no meaningful distinction and therefore upheld exclusion under Rule 704(b). Because the rule was correctly applied, Herrera’s constitutional argument failed in the absence of any “compelling reason” to override the evidentiary scheme.

Impact

This decision reaffirmed the Eleventh Circuit’s strict application of Rule 704(b) in § 2422(b) enticement prosecutions:

Defense counsel must carefully tailor expert testimony on psychosexual assessments to avoid directly opining on a defendant’s mental state or intent.
Experts may still testify on related topics—such as diagnostic criteria for autism spectrum disorder or general behavioral traits—but must stop short of stating ultimate conclusions about mens rea.
Future litigants in the Eleventh Circuit will face significant hurdles when seeking to admit expert opinions that intersect with the specific intent elements of child‐enticement statutes.

Complex Concepts Simplified

Rule 704(b) in Plain Terms: In criminal trials, only the jury decides whether the defendant had the required state of mind (e.g., knowingly, willfully). Experts can explain mental health diagnoses or describe behaviors, but cannot say “I conclude the defendant did or did not have that state of mind.”

“Ultimate Issue”: The question the jury must resolve to find guilt. In an enticement case, that includes whether the defendant knowingly tried to lure a minor into sexual activity.

Psychosexual Assessment: A clinical evaluation that examines sexual history, preferences, and potential paraphilias. Useful background information, but an expert cannot leap from those findings to a definitive statement about criminal intent.

Conclusion

United States v. Joshua Herrera underscores the Eleventh Circuit’s rigorous enforcement of Rule 704(b) in federal child‐enticement prosecutions under 18 U.S.C. § 2422(b). Drawing on the binding Gillis precedent, the court confirmed that expert testimony affirming a defendant’s lack of sexual interest in minors improperly invades the jury’s province to decide mens rea. Practitioners must navigate these evidentiary limits by focusing on permissible expert insights—such as mental health diagnoses and behavioral traits—while avoiding direct opinions on ultimate intent. This ruling solidifies the rule that, even as defendants have a constitutional right to present a defense, that right does not extend to expert conclusions on the precise mental-state element of the crime.