Special counsel Robert Mueller says former Trump campaign chairman Paul Manafort attempted to tamper with potential witnesses and has asked the court to rescind or revise Manaforts pretrial release.

In a court filing Monday, Mueller said there was probable cause to believe Manafort tried to reach witnesses using an encrypted messaging program in an effort to suborn perjury while he was awaiting trial, one of the witnesses told federal investigators.

Manafort was indicted in October on a dozen charges, including conspiracy against the United States in connection with lobbying work he conducted for Ukraine. New charges linked to tax and bank fraud were filed by the special counsels office in February.

He was released to home confinement in October while awaiting his trial, which is expected to begin Sept. 17.

The special counsels Monday filing relies on a declaration from FBI Special Agent Brock Domin, who said that earlier this year Manafort and one of his associates had attempted to contact two unnamed members of The Hapsburg Group, a firm he worked with while lobbying for his Ukrainian clients.

Manafort and Person A who is a longtime associate of Manaforts repeatedly contacted Persons D1 and D2 in an effort to secure materially false testimony concerning the activities of the Hapsburg group, the court filing reads.

At one point, Manafort sent one of the unidentified people a text via an encrypted messaging service that read, This is paul, before sending a message linking to a news article and another saying, we should talk.

After the two people ignored several messages or hung up on Manaforts calls, his associate attempted to contact them for him. My friend P is trying to reach [Person D1] to brief him on whats going on, one of the messages sent by the associate in February read.

Several months later, the associate sent another message to a different person reading: My friend P is looking for ways to connect to you to pass you several messages. Can we arrange that.

Domin said the two potential witnesses believed the messages and phone calls were an effort to influence [their] testimony.

Mueller pointed to the evidence in his calls for the courts to promptly schedule a hearing to revise Manaforts release, saying his actions threaten the integrity of the trial.

Manaforts obstructive conduct carried out at a time when he was seeking relief from his current conditions of release instills little confidence that restrictions short of detention will assure Manaforts compliance with the Courts orders and prevent him from committing further crimes, the filing reads.

This article has been updated with more details from the court filing.