A billion-dollar fund belonging to a Russian government official and invested in U.S. public companies has been frozen by the Treasury department after an investigation going back more than a year.

The Treasury Department issued a blocked property notice to Heritage Trust, a Delaware-based fund that the department says belongs to Suleiman Kerimov, a member of the Federation Council of the Federal Assembly of Russia. Kerimov had initially been sanctioned in 2018, and the FBI helped to seize one of his yachts in Fiji in May.

A senior Treasury official said that money from the trust was invested in numerous large U.S. public corporations and private companies after being moved through layers of shell companies, European foundations, and other identity-obscuring legal entities.

The official declined to comment on whether any U.S. law firms, accounting firms or consultancies may be complicit in helping the fund do its business and administer its investments.

The blocked property notice from the Treasury’s Office of Foreign Assets Control (OFAC) doesn’t mean that Kerimov’s money is being seized by the U.S. government. It means that any transactions involving the trust’s money or property are now illegal and subject to prosecution.

“All transactions by U.S. persons within (or transiting) the United States that involve any property or interests in property of designated or otherwise blocked persons are prohibited,” the department said in a statement.

Following Russia’s invasion of Ukraine in late February, the U.S. set up an international task force, known as REPO (Russian Elites, Proxies, and Oligarchs), to pursue the assets of the Russian elite in order to pressure Russian president Vladimir Putin and the architects of Russia’s foreign and military policy. 

The task force included financial and legal branches of the governments of Australia, Canada, Germany, France, Italy, Japan, the United Kingdom, and the European Commission, and represents the broader cooperation among Western powers resulting from the war in Ukraine.

Treasury Secretary Janet Yellen said in a statement that “even as Russian elites hide behind proxies and complex legal arrangements, Treasury will use our broad enforcement authorities, as well as our partnerships through the REPO Task Force, to actively implement the multilaterally coordinated sanctions imposed on those who fund and benefit from Russia’s war against Ukraine.”

During a State Department summit last year, Yellen called out the U.S.’s labyrinthine set of laws that allow for the whitewashing of dirty money.

“In the popular imagination, the money laundering capitals of the world are small countries with histories of loose and secretive financial laws. But there’s a good argument that, right now, the best place to hide and launder ill-gotten gains is actually the United States. And that’s because of the way we allow people to establish shell companies,” Yellen said.

Earlier this year, the U.S. topped a list of the most financially secretive countries in the world, beating out the likes of Switzerland, the Cayman Islands and other notorious tax havens.

British advocacy group the Tax Justice Network reported in May “that the supply of financial secrecy services, like those utilised by Russian oligarchs, tax evaders and corrupt politicians, has continued to decrease globally due to transparency reforms. But five G7 countries alone – the US, UK, Japan, Germany and Italy – are responsible for cutting global progress against financial secrecy by more than half.”

While Kerimov’s asset freezing shows that international authorities are sometimes able to navigate the U.S.’s legal mazes, it’s not clear how much more Russian money could be hidden in the U.S. financial system.