Mattson v. Rosebud Electric Cooperative
U.S. District Court, District of South Dakota, Central Division · D.S.D. · South Dakota bar guidance
Conduct
Pro se plaintiffs filed PURPA/RICO response brief with fictitious cases, incorrect citations, and AI-suggesting formatting.
Consequence
Motion to dismiss granted in full; no Rule 11 sanction imposed because plaintiffs filed timely correction.
Lesson
D.S.D. now treats prompt self-correction of AI-generated citations as a sanction-mitigation factor, not a free pass.
Verified May 7, 2026
- Citation
- Mattson v. Rosebud Elec. Coop., No. 3:25-cv-03008-RAL (D.S.D. Nov. 17, 2025) (Lange, C.J.)
- Decided
- November 17, 2025
Summary
Pro se plaintiffs Thomas Mattson and Edward J. Dostal filed a complaint against Rosebud Electric Cooperative, Grand Electric Cooperative, Basin Electric Power Cooperative, and Moreau-Grand Electric Cooperative asserting PURPA, RICO, and Sherman Act claims related to the non-development of twelve qualifying-facility wind farms. Defendants' reply brief identified that "Plaintiffs' response brief contains fictitious cases, incorrect case citations, and non-existent quotations," documenting inconsistencies between Plaintiffs' citations and the actual case law. Plaintiffs filed a "Notice of Corrected Citations" and a sur-reply asserting the corrected citations were "either direct verbatim excerpts or faithful paraphrases of the controlling principles."
- AI tool:
- Implied (court found 'the formatting of the brief, which seemed to suggest the use of generative AI')
What sanction did the court impose?
Chief Judge Roberto A. Lange granted defendants' motion to dismiss in full. Counts 1, 2, 3, 5, 6, 7, 9, and 11 were dismissed without prejudice; counts 4, 8, and 10 with prejudice. As to the fictitious citations, the court declined to impose sanctions: "In reviewing Plaintiffs' Response, this Court noted the formatting of the brief, which seemed to suggest the use of generative AI, as well as the inclusion of incorrect case citations and quotations. Plaintiffs corrected their filing, and this Court is disinclined to sanction these pro se Plaintiffs for improper citations, though they should review and abide by Federal Rule of Civil Procedure 11(b) for future filings."
Why does Mattson v. Rosebud Electric Cooperative matter for law firms using AI?
Chief Judge Lange declined sanctions because plaintiffs cured before the court ruled. After defendants flagged fabricated citations in their reply, plaintiffs filed a Notice of Corrected Citations. That filing arrived ahead of the dismissal order. Lange still flagged on the record that “the formatting of the brief, which seemed to suggest the use of generative AI” contributed to his suspicions. Defendants documented multiple fictitious citations and non-existent quotations across a 51-page response brief. Plaintiffs’ sur-reply certified all citations as “direct verbatim excerpts or faithful paraphrases.”
This is the first published D.S.D. opinion engaging with AI-generated court filings. The no-sanction outcome rests on one procedural move: correction before ruling.
Dismissal still ran in defendants’ favor across the board. Counts 4, 8, and 10 went out with prejudice. Count 11 had sought sanctions against defendants for prior litigation misconduct in unrelated forums, and Lange rejected it as procedurally improper under Rule 11’s separate-motion requirement. Plaintiff Mattson had previously litigated these claims through Prelude LLC. A federal judge in the Eastern District of Wisconsin had held Prelude could not appear pro se as a corporation, prompting Mattson to assign the claims to himself for $1. Lange held that assignment did not circumvent the corporate-representation rule. Two practical signals emerge for South Dakota firms. Pro se AI-formatted briefs are now within the court’s pattern recognition, and the corrective-filing pathway works only if it precedes the order.
Implications for your firm
Operational steps a firm reading this case may wish to consider documenting. Strategic and rule-application calls belong to your firm's attorneys.
- Cite Mattson when advising D.S.D. clients that a Notice of Corrected Citations filed before the court rules can preserve the no-sanction outcome even on AI-formatted briefs.
- Treat Chief Judge Lange's 'formatting suggested AI' finding as the standard benchmark: brief structure itself can support an AI inference without an admission.
- When opposing pro se plaintiffs in D.S.D., document fabricated citations in your reply rather than waiting for the court to find them: defendants here did the work and the court relied on their inventory.