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(CNN) —  

A court filing from special counsel Robert Mueller signals that Rick Gates may be assisting the investigation into Russian interference in the 2016 election beyond the case against Paul Manafort.

In a filing Thursday, Mueller’s team said it wanted to keep a discussion between trial attorneys and Judge T.S. Ellis regarding a question to Gates secret because the transcript of the conversation would “reveal details of the ongoing investigation.”

When Gates pleaded guilty and flipped on Manafort in February, he also agreed to help the special counsel with its investigation into Russian election interference as he was needed. It’s unclear how he has aided the special counsel’s probe beyond the Manafort case, but Gates was a deputy to Manafort on the Trump campaign and worked on the transition and presidential inauguration.

The still-secret conversation occurred Tuesday afternoon in the middle of Gates’ testimony against Manafort, who served as Trump’s campaign chairman in 2016.

Defense attorney Kevin Downing had asked Gates, “Were you interviewed on several occasions about your time at the Trump campaign?”

Prosecutor Greg Andres objected to the question before Gates could answer.

The lawyers and Ellis then huddled in the far corner of the courtroom to discuss whether the question could be asked. The courtroom’s overhead noise machine was turned on so that Gates, the jury and the public in the room couldn’t hear what they said.

Ellis called for a break in the proceedings immediately after the short discussion ended, and Downing tried to ask about the Trump campaign investigation again.

During the discussion – one of many during a trial, often called a “sidebar conference” in court lingo – the prosecutors now say they discussed “new” details about their “ongoing criminal investigation” into Russia’s interference in the 2016 presidential election and possible coordination with the Trump campaign.

“Disclosing the identified transcript portions would reveal substantive evidence pertaining to an ongoing investigation … In addition, sealing will minimize any risk of prejudice from the disclosure of new information relating to that ongoing investigation,” the special counsel’s team wrote in a court filing Thursday. “The government’s concerns would continue until the relevant aspect of the investigation is revealed publicly, if that were to occur.”