On Monday, Robert Mueller accused Paul Manafort in court filing of tampering with potential witnesses during his pre-trial release.

Manafort Accused of Attempted Witness Tampering

A judge has set a June 15 date for a hearing on the special counsel’s request to send Manafort — President Donald Trump‘s former campaign chairman — to prison on charges related to the allegations.

In records filed Monday evening, the special counsel claimed Manafort tampered with two potential witnesses against him. Manafort has pleaded not guilty to a previous set of charges — as part of Mueller’s Russia investigation — that include money laundering and tax fraud.

Mueller has now alleged Manafort, 69, attempted to “suborn perjury,” or bribe witnesses to hide evidence pertaining to his upcoming trials while he was still under house arrest in his Virginia mansion. The special counsel has requested that Manafort’s $10 million release bail be revoked in order to send him to jail.

Manafort is set to appear in court in Virginia beginning July 24, and will then face trial in Washington in September. The former Trump campaign chair is accused of performing lobbying work for several Ukrainian political candidates with ties to pro-Russia parties.

Former Trump aide Rick GatesManafort’s business partner, pleaded guilty to conspiracy and lying to federal investigators in February. Manafort’s former son-in-law Jeffrey Yohai was also recently charged in a major real-estate case.

In a pair of tweets on Sunday, Trump accused the FBI and Justice Department of “secretly investigating” Manafort on a series of old charges. The president also said that had he known investigators were doing this, he would not have hired Manafort.

In addition to Manafort, former national security adviser Michael Flynnformer Trump adviser George Papadopoulos and Dutch lawyer Alex van der Zwaan have all pleaded guilty in the Russia probe.