Russian executives hoping to prevent past business transactions with U.S. President Donald Trump from becoming public knowledge will get found out sooner or later, according to a professor at John Hopkins University.

“I think everybody in Russia who has done business with Trump is going to get found out at some point,” Erik Jones, professor of European studies and international political economy at Johns Hopkins University, told CNBC on Friday.

Trump has consistently dismissed the sustained public and political pressure to release his tax returns and, while there is no law compelling the U.S. President to do so, the former New York businessman broke a long-held tradition when he decided not to release his paperwork during the presidential campaign.

In a letter released by the White House on May 12, Trump’s lawyers said a review of the president’s tax returns found that with a “few exceptions”, he had not received any income from Russian business contacts over the past decade. However, the attorneys did not release copies of the documents.