Reported / Citable
Background
Mario Chapa was charged in federal court with receipt and possession of child pornography under 18 U.S.C. §§ 2252A(a)(2) and 2252A(a)(5)(B). The charges arose from a search of his San Antonio apartment on April 7, 2022, which yielded two hard drives containing a large volume of child sexual abuse material (CSAM). The search was conducted pursuant to a federal warrant issued on April 4, 2022, by U.S. Magistrate Judge Henry J. Bemporad.
The investigation was part of a coordinated FBI effort targeting the Freenet peer-to-peer network, which is designed to anonymize users’ online identities by breaking files into encrypted blocks distributed across network nodes. FBI agents used law enforcement computers on the Freenet network to passively log incoming file requests, employing the “Levine Method” — a statistical algorithm developed by Dr. Brian Levine of the University of Massachusetts Amherst — to determine whether a given node was the original requestor of a known CSAM file rather than merely relaying another user’s request. Between May and July 2021, FBI nodes observed an IP address later traced via subpoena to Chapa requesting blocks of three known CSAM files.
Chapa moved to suppress the evidence, arguing that FBI Special Agent James Thompson had made materially false or reckless statements in the warrant affidavit, and seeking a full evidentiary hearing under Franks v. Delaware, 438 U.S. 154 (1978). Specifically, Chapa challenged paragraphs of the affidavit describing how Freenet routes file requests and how the Levine Method’s statistical assumptions operate, contending the descriptions were inaccurate and that defense testing in 2023 and 2025 revealed false-positive rates inconsistent with Dr. Levine’s published findings.
The Court’s Holding
Judge Xavier Rodriguez denied Chapa’s motion for a Franks hearing. The court found that Chapa failed to make the required preliminary showing that Agent Thompson included deliberate falsehoods or reckless misrepresentations in the warrant affidavit. Reviewing each challenged paragraph, the court concluded that Thompson’s descriptions of Freenet’s routing mechanics and the Levine Method were lay-level summaries consistent with Dr. Levine’s 2020 peer-reviewed paper, appropriately hedged with language such as “roughly” and “for example,” and anchored by a direct citation to that study.
The court rejected Chapa’s argument that simplifying assumptions in the affidavit — such as characterizing request distribution as “roughly equal” among peers — amounted to material falsehoods. The court credited Dr. Levine’s explanation that the method’s validity rests on its empirically measured low false-positive rate across 918 real-network experiments conducted over four years, and that simplifying assumptions are standard scientific practice. The court found that defense counsel’s own subsequent testing, and the defense expert’s disagreement with Levine’s methodology, demonstrated a scientific dispute — not evidence that Thompson acted with reckless disregard for the truth.
Applying Franks‘ presumption of validity and the commonsense reading standard from Illinois v. Gates, 462 U.S. 213 (1983), the court concluded that Chapa’s showing was insufficient to overcome that presumption. Because the affidavit’s challenged content, viewed fairly, was not false or reckless, no evidentiary hearing was required.
Key Takeaways
- To obtain a Franks hearing, a defendant must make a substantial preliminary showing of deliberate falsehood or reckless disregard for the truth by the affiant — allegations of negligence, innocent mistake, or mere scientific disagreement are insufficient.
- A law enforcement agent’s lay-level simplification of a peer-reviewed scientific methodology in a warrant affidavit does not constitute a material misrepresentation where the affidavit cites the underlying study and uses appropriately qualified language.
- Defense expert testimony and post-warrant testing that conflict with the government’s scientific method may establish a good-faith scientific dispute but do not, without more, demonstrate that the affiant acted with reckless disregard for the truth at the time of the warrant application.
- Courts affirm the Levine Method as a legally adequate basis for probable cause in Freenet-based CSAM investigations, consistent with decisions in other circuits.
Why It Matters
This decision reinforces the legal viability of FBI investigations using the Levine Method on the Freenet network — one of the primary technical tools federal agents deploy in CSAM cases involving anonymizing peer-to-peer software. Defense challenges to the method have proliferated as more cases reach the suppression stage, and courts across the country have grappled with whether the statistical assumptions underlying the algorithm can support probable cause. The Western District of Texas here joins other courts in holding that the method withstands scrutiny and that warrant affidavits relying on it need not achieve scientific precision to satisfy Franks.
For practitioners, the ruling draws a sharp line between attacking the scientific validity of a law enforcement technique (which may be explored at trial) and meeting the high bar required to void a warrant under Franks (which demands proof of the affiant’s deliberate or reckless dishonesty). Defense attorneys challenging Freenet-based warrants will need more than competing expert opinions and post-hoc testing — they must marshal evidence bearing directly on the affiant’s state of mind at the time of the application.