According to the DoJ press release:

A Montana man was sentenced today to six months in prison for committing two felony wildlife crimes — a conspiracy to violate the Lacey Act and substantively violating the Lacey Act — as part of an almost decade-long effort to create giant sheep hybrids in the United States with an aim to sell the species to captive hunting facilities.

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Schubarth brought parts of the largest sheep in the world, Marco Polo argali sheep (Ovis ammon polii), from Kyrgyzstan into the United States without declaring the importation. Average males can weigh more than 300 pounds, with horns that span more than five feet. Marco Polo argali are native to the high elevations of the Pamir region of Central Asia. They are protected internationally by the Convention on International Trade in Endangered Species (CITES) and domestically by the Endangered Species Act, and are prohibited in the State of Montana to protect native sheep from disease and hybridization.

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“Schubarth not only violated federal and state law and international treaties, but he and others illegally conspired to conceal their actions from authorities,” said Assistant Attorney General Todd Kim of the Justice Department’s Environment and Natural Resources Division. “Violations of the Lacey Act, CITES and other laws can be devastating for our domestic populations of wild animals, which is why we are unwavering in our commitment to enforce them.”

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The Lacey Act prohibits interstate trade in wildlife that has been taken, possessed, transported or sold in violation of federal or state law. The Lacey Act also prohibits the interstate sale of wildlife that has been falsely labeled. The Act is one of the most powerful tools the United States has to combat wildlife trafficking and prevent ecological invasion by injurious wildlife.

So while he violated a raft of international, regional and state laws, it was the Lacey Act that they used to convict him.