Washington (CNN) A defense attorney for Andrew Miller, who's fighting a subpoena from Robert Mueller's investigation into Russian interference in the 2016 election, learned Monday afternoon that the special counsel still wants witness testimony for a federal grand jury.

Paul Kamenar, the defense attorney, says the assertion from Mueller's team made clear to him that Mueller and the Justice Department are considering an additional indictment of Roger Stone or have plans to charge others.

The development sets up the potential for another twist in the Russia probe. It comes hours after acting Attorney General Matthew Whitaker said that Mueller's investigation was "close to being completed."

Kamenar's client is Miller, a former employee of Stone's whom Mueller subpoenaed in mid-2018 to testify to the grand jury. In a court hearing about Miller's testimony, a judge made clear that Mueller sought information Miller had about Stone's communications regarding Wikileaks and Russian hackers around the time they disseminated damaging hacked Democratic emails.

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