Claude (Sonnet 4). Invented quotations attributed to real Supreme Court and circuit opinions.
Gurpreet Kaur was detained by immigration officials after crossing the Canadian border. Her attorney, Dennis Desmarais, filed a habeas petition and an emergency motion to stop her removal to India.
His supplemental brief contained fabricated quotations from real Supreme Court decisions, including DHS v. Thuraissigiam and Landon v. Plasencia. The government's brief flagged the false quotes, and the Court's own review found more in citations to Reno v. American-Arab Anti-Discrimination Committee and Wong Wing. At a hearing, Desmarais admitted he used the generative AI tool Claude Sonnet 4 to draft the brief and did not check its work.
Offered for: a due-process limitation on a holding
The Court found that Desmarais violated Rule 11 and acted in subjective bad faith, since he knew AI tools can fabricate citations yet did not verify them. It imposed a $1,000 penalty payable to the Clerk of Court within 14 days and ordered him to file proof of completing a CLE program on the use of AI in legal writing, and proof of serving the order on the petitioner, by September 1, 2025.
Kingsfield returned REJECT. The brief quotes Thuraissigiam as saying a sentence that is not in the decision. The court confirmed the quoted line appears nowhere in it.
This matter is among the US case-law cases we ran Kingsfield against in the Charlotin benchmark. Kingsfield's existence check confirms every citation against the case-law corpus and an independent source (CourtListener) before any claim resting on it can stand. Across the run Kingsfield ruled 696 of 700 testable claims correctly, including every one of the 504 fabricated citations and 92 fabricated quotes.
Honest scope. This measures Kingsfield's ruling layer given an extracted citation, not an end-to-end run over a full brief. The case record and the AI-tool attribution come from Damien Charlotin's public database and the court order; the verdict is Kingsfield's. See the full 700-claim benchmark.