Federal prosecutors on Friday told a judge the U.S. government has “thousands of intercepts” involving Dmitry Firtash, a Ukrainian oligarch with ties to former Donald Trump campaign chairman Paul Manafort, the Chicago Tribune reports.

The claim was made during an extradition hearing in Chicago. In 2014, Firtash was picked up by authorities in Austria after a Virginia judge issued a warrant for his arrest. In April, he was indicted on charges of bribery and money laundering stemming from an international titanium mining racket scheme. Lawyers have been fighting his extradition from Vienna for over three years.

In addition to having ties to Manafort, Firtash is also linked to Vladimir Putin. As Reuters reports, banks with ties to the Kremlin lent Firtash up to $11 billion to help back former Ukranian president Viktor Yanukovich, a Putin ally.