Alexandria, Virginia (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?"

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