Special counsel Robert Mueller asked a federal judge Tuesday to grant immunity to five unidentified potential witnesses whose testimony he wants to compel at the criminal trial of ex-Trump campaign chair Paul Manafort, CNBC reported Tuesday, citing court documents.

Without immunity from prosecution, the five could refuse to testify, or invoke their Fifth Amendment right against self-incrimination, according to Mueller’s filing in federal court in Alexandria, Va.

Mueller also asked Judge T.S. Ellis to seal the court motions listing the witnesses’ identities to prevent their identities from being publicly disclosed.

“The five individuals identified in the motions at issue are third parties who have not been charged in this matter, and who have not been identified publicly with the case,” Mueller’s team argued in the filing, the network reported.

“Disclosing the motions would reveal those individuals’ involvement in the investigation and the trial, thereby creating the risk of their undue harassment.”

Manafort’s trial on money laundering and other corruption charges is set to begin July 25.