A mysterious U.S. probe into a firm once controlled by Russian billionaire Oleg Deripaska has reportedly been revealed in British court filings. Bloomberg reports the company, Terra Services, was raided as part of a previously-undisclosed investigation sparked by the findings of Special Counsel Robert Mueller. Bloomberg states that U.S. prosecutors are seeking evidence of “money laundering, tax offenses and fraud offenses” at the firm. The “live and ongoing” probe was revealed by documents filed in a London court after Terra Services challenged a search warrant that led to the seizure of 25,000 documents from a British storage unit last year. Terra has asked a London judge to stop the documents from being given to U.S. authorities, with the company saying that it believed the search request was made “in connection with the special counsel investigation being conducted in the U.S.” Mueller’s report stated that former Trump campaign chairman Paul Manafort offered Deripaska briefings and internal polling data. Deripaska remains under U.S. sanctions.