Washington (CNN) An associate of Roger Stone has agreed to testify to special counsel Robert Mueller's grand jury on Friday morning, his attorney and a Mueller prosecutor said in a court hearing before a federal judge.

The development shows parts of the Mueller investigation related to interference in the 2016 presidential election -- and the grand jury's work -- may still be alive.

Andrew Miller, Stone's associate, has fought testifying as he has challenged Mueller's authority since last summer after Mueller's team requested information from him about Roger Stone and WikiLeaks. Miller was held in contempt by Chief Judge Beryl Howell in Washington but will not be sent to jail at this time, the judge said. He lost his attempts at appeal. He did not attend the hearing Wednesday.

One Mueller prosecutor, Aaron Zelinsky, who has led the case against Stone along with prosecutors from the DC US Attorney's Office, was in court Wednesday morning regarding Miller. During the hearing, Zelinsky and Jonathan Kravis from the US Attorney's Office in DC told the judge privately why they still needed Miller.

Zelinsky declined to comment about the case outside of the hearing or about Mueller's public statement at the Justice Department Wednesday. Zelinsky also declined to tell CNN what part of the Justice Department he's currently working in, minutes after Mueller announced the Special Counsel Office's closure.

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