Washington (CNN) The grand jury's criminal investigation started by special counsel investigators is "continuing robustly," a federal prosecutor said Wednesday, even though Robert Mueller filed his report on Russian interference in the 2016 election with the Justice Department last week.

In a federal court hearing about whether the name of a foreign-owned company and the country that's been fighting a subpoena from Mueller since last summer should be revealed, Chief Judge Beryl Howell asked prosecutor David Goodhand point-blank if the grand jury investigation is over.

"No, it's continuing. I can say it's continuing robustly," said Goodhand, an assistant prosecutor in the DC US Attorney's office.

It remains unclear what part of Mueller's investigation is ongoing and if more criminal charges could still come, but the hearing on Wednesday made clear that stones Mueller turned over in the last 22 months will continue to be part of federal court proceedings and possibly lead to new cases.

There were no prosecutors from Mueller's office in court. The special counsel's office has handed over the subpoena case to the DC US Attorney's office.

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