The Denver-based federal appeals court warned attorneys to be more careful last month after discovering one lawyer cited a fake case in his arguments.

In recent months, federal and state judges in Colorado have begun cautioning lawyers explicitly about the pitfalls of using generative artificial intelligence in legal filings without verifying the output. The Colorado Supreme Court recently amended the rules of professional conduct to warn about the potential violations lawyers may trigger with improper AI use. Within weeks of each other last fall, two federal judges also called out fake citations that appeared in legal filings.

In early February, the U.S. Court of Appeals for the 10th Circuit ordered a lawyer to pay $1,000 for her “reckless” inclusion of fake cases in her appeal.

On Feb. 13, a three-judge panel for the 10th Circuit rejected an asylum appeal in a family’s Colorado-based immigration proceedings. The panel determined the family of five had not established a likelihood of future persecution in Colombia based upon a relative’s ongoing extortion by a criminal organization.

“If counsel made a citation error, we have not been able to deduce what it might be. We have not uncovered any relevant federal case similarly captioned or containing any of the quotations that counsel attributes to this apparently nonexistent case,” wrote Senior Judge Paul J. Kelly Jr. in the panel’s order. “This case citation and the quotations and propositions attributed to it appear fabricated. This is likely the result of Petitioners’ counsel’s use of a generative artificial intelligence tool as a research and drafting aid without adequate review of the results the tool generated.”

The family’s attorney cited to a 2023 decision of the 10th Circuit, and explained why its contents supported his clients’ position. However, the government pointed out in its response that the case was fictional.

In determining whether to impose consequences, Kelly acknowledged there was nothing “inherently problematic” with using AI, so long as an attorney does not attempt to persuade a court with fake cases.

“However, we decline to sanction counsel in this case but warn him — and all attorneys practicing before this court — of the responsibility to ensure that citations to legal authority are not fabrications but instead point to real cases that contain quotations attributed to them and arguably stand for the propositions for which they are cited,” Kelly concluded.

The attorney, Jorge E. Munoz of Houston, confirmed the 10th Circuit’s description of the problem.

“This occurred because I used an AI research tool and failed to adequately verify the results before filing. I take full responsibility for this error,” he told Colorado Politics. “I have implemented verification procedures to independently confirm all cited authorities before submission and to ensure this does not happen again.”

The case is Picon-Diaz et al. v. Bondi.