United States v. David Lieu, 963 F.3d 122

Lieu engaged online with an account (“John”) he believed was a father of a nine‑year‑old; the respondent was actually an FBI undercover agent. Lieu exchanged sexually explicit messages and images and agreed to meet in D.C. to perform sexual acts on the purported nine‑year‑old. He traveled from Maryland to D.C. and was arrested on arrival.
Agents seized Lieu’s computer and phone; the computer contained hundreds of child‑pornography images and the phone contained the explicit chats with the undercover agent and another party.
Lieu’s stepdaughter ("E.") reported that Lieu had touched her genitals and otherwise assaulted her when she was between six and eight; E. testified at trial.
Lieu was charged with distribution of child pornography, 18 U.S.C. § 2252(a)(2), and traveling in interstate commerce with intent to engage in illicit sexual conduct with a minor, 18 U.S.C. § 2423(b).
The district court admitted E.’s testimony under Fed. R. Evid. 404(b) (intent/knowledge/absence of mistake) and Fed. R. Evid. 414 (other child‑molestation evidence), and concluded under Rule 403 that its probative value outweighed any unfair prejudice.
Lieu moved to dismiss the travel count (arguing the intended victim did not exist) and appealed the admission of E.’s testimony; the court of appeals affirmed both rulings and Lieu’s convictions.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether § 2423(b) criminalizes interstate travel when the defendant intended to molest a child who in fact did not exist	United States: § 2423(b) is satisfied because Lieu traveled with intent to engage in illicit sexual conduct with a child as he believed one existed; impossibility is not a defense	Lieu: statute requires an actual other person; because the purported nine‑year‑old was fictitious, no travel offense occurred	Court: Affirmed — § 2423(b) is satisfied by the defendant’s intent to engage in illicit sexual conduct with a child as he believed one to exist; factual impossibility is not a defense (aligns with circuit precedent)
Whether the district court abused its discretion by admitting E.’s testimony under Rules 404(b)/414 despite Rule 403 prejudice concerns	United States: E.’s testimony is highly probative of intent, knowledge, absence of mistake, and—under Rule 414—propensity on the distribution count; limiting instructions and the relative non‑graphic nature reduce unfair prejudice	Lieu: the prior abuse was remote and dissimilar, risked an improper propensity inference, and was unfairly prejudicial; timing of limiting instruction was improper	Court: Affirmed — district court did not abuse discretion; E.’s testimony was significantly probative of Lieu’s sexual interest in young girls and state of mind, prejudice was minimal, and limiting instructions addressed misuse

United States v. Williams, 553 U.S. 285 (impossibility is not a defense to inchoate offenses; assess defendant's belief)
United States v. Tykarsky, 446 F.3d 458 (3d Cir.) (§ 2423(b) applies even if an actual minor was not involved)
United States v. Sims, 428 F.3d 945 (10th Cir.) (rejecting defense based on nonexistence of purported child)
United States v. Root, 296 F.3d 1222 (11th Cir.) (conviction rests on illegal purpose to travel)
United States v. X‑Citement Video, Inc., 513 U.S. 64 (knowledge-of-age issues in child‑pornography prosecutions)
United States v. Long, 328 F.3d 655 (D.C. Cir.) (admissible bad‑acts evidence need not be identical; limits on propensity inference)
United States v. Cassell, 292 F.3d 788 (D.C. Cir.) (Rule 403 exclusion standard imposes high barrier)
United States v. Hite, 769 F.3d 1154 (D.C. Cir.) (standards of appellate review for statutory questions)