Washington (CNN) Ever since reaching a deal with special counsel Robert Mueller, Paul Manafort has kept the Russia prosecutors busy.

The former Trump campaign chairman and his lawyers have visited Mueller's office in Washington at least nine times in the last four weeks, a strong indication that the special counsel is moving at a steady clip.

September and October at first glance appear to be quiet periods for the investigation, under the Justice Department's guidelines to avoid public political acts before the midterm elections. But the quiet period has seen a persistent murmur of activity, based on near-daily sightings of Mueller's prosecutors and sources involved in the investigation.

In addition to Manafort, Mueller's team has kept interviewing witnesses, gathered a grand jury weekly to meet in Washington on most Fridays, and kicked up other still-secret court action. Plus, the discussions between the President's legal team and the special counsel's office have intensified in recent weeks, including after the special counsel sent questions about possible collusion between the Trump campaign and Russian government. The President's attorneys are expected to reply to the questions in writing.

People around Trump and other witnesses believe more criminal indictments will come from Mueller.

Attorneys who have dealt with Mueller's investigators and other officials expect that the special counsel's efforts, now 17 months in the works, will include an active post-election period a much-anticipated report where Mueller will outline what his investigators decided to prosecute and what they declined.

Deputy Attorney General Rod Rosenstein, who oversees the investigation, on Wednesday called the probe "appropriate and independent," in an interview with The Wall Street Journal.

"[A]t the end of the day, the public will have confidence that the cases we brought were warranted by the evidence and that it was an appropriate use of resources."

A frequent cooperator

At least nine times since he pleaded guilty on September 14, a black Ford SUV has brought Manafort to Mueller's office in southwest DC around 10 am. Manafort's lawyers arrive around the same time, waiting in the lobby for the car to arrive. There they remain inside the offices, typically for six hours.

It's not entirely clear yet what Manafort has shared with prosecutors, and if his interviews check facts that haven't yet come to light outside of the prosecutors' own notes. Among the questions, investigators have asked Manafort about his dealings with Russians, according to one source familiar with the matter.

Attorneys for Manafort would not discuss their activities for this story.

The visits amount to what could total dozens of hours of interviews between Mueller's prosecutors and Manafort since he finalized his plea agreement. Manafort agreed to fully cooperate with the Justice Department as it investigates the Trump campaign and the Russian government's actions before the 2016 election.

At the same time, Trump has distanced himself from crimes investigators still may be pursuing. He publicly claimed this week that criminal charges so far brought by Mueller's team have nothing to do with him. Trump attorneys declined to comment for this story.

Other help

The flurry of interviews with Manafort and other cooperating defendants leaves Trump's legal team somewhat in the dark on what Mueller is pursuing.

Manafort's lawyers have shared information with the Trump legal team, but according to sources familiar with the case, there is no formal joint defense agreement.

Manafort's criminal confessions and separate conviction by a jury dealt with his Ukrainian lobbying work and financial dealings largely before 2016. Yet his cooperation is widely expected to include helping the prosecutors build potential criminal cases about coordination between the Russian government and Trump campaign.

Aside from Manafort, three other Trump campaign officials have pleaded guilty to charges. Two of them, campaign deputy Rick Gates and former national security adviser Michael Flynn, also agreed to broadly help Mueller's team with its investigation and have visited the special counsel's office to give interviews since their pleas.

Mueller's team has also been speaking with Michael Cohen , Trump's former personal attorney, who has spent hours with Mueller's team since his own guilty plea in August, in which he accused President Donald Trump of directing him to commit a crime.

Trump legal team

Meanwhile, Trump's team is working up answers to Mueller's questions. Even if the defense team were to sign and deliver their answers soon, Mueller's office may have follow-up questions that drag out their discussions. The legal team, comprised of personal and White House lawyers Jay Sekulow, Marty and Jane Raskin and Emmet Flood, still hasn't reached an agreement on whether the President will be interviewed in person or must respond to questions about possible obstruction of justice related to his firing of FBI Director James Comey.

While they're in investigatory limbo, expectations have grown in Washington legal circles that Mueller will issue a report soon after the November election or even before the end of the year.

When it's finished, Mueller's report is expected to explain the decisions of the Justice Department to bring or to decline to bring criminal cases during the course of the investigation. Mueller's findings and decisions will be confidential, unless higher-up officials in the Justice Department decide to make the report public.

As of now, the Trump legal team operates under the belief that Mueller won't finish his work without bringing indictments that hit closer to the Trump campaign.

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Activity in the DC courthouse

The next campaign contact in Mueller's crosshairs may be Trump adviser Roger Stone, who's publicly said he expects to be indicted after nine of his friends and aides spoke to Mueller's office or received grand jury subpoenas. In the last two weeks, multiple contacts of Stone have been in touch with the special counsel's office about them providing information, according to CNN's reporting.

Special counsel prosecutors have also visited the federal courthouse in downtown Washington almost daily.

Once in early September and once in early October, Chief Judge Beryl Howell held hour-long sealed hearings in her courtroom featuring trial and appellate prosecutors from Mueller's office. Both times, the lawyers opposite the Justice Department declined to share with CNN their names, clients names or law firms. Howell oversees court action related to the federal grand jury that Mueller has used to approve indictments in DC.

Previously she has ordered two witnesses -- a real estate agent and a lawyer -- to testify against Manafort before the grand jury, and she held Andrew Miller, a Stone associate, in contempt for refusing to comply with a subpoena. The real estate and lawyer orders became public on the eve of Manafort's indictment last October, and Miller's attorneys spoke publicly about his subpoena challenge as it was ongoing.

Other times in the courthouse in recent weeks, the Mueller investigators visit the chief judge's chambers and then clerk's office, indicating a flurry of court paperwork.

A spokesperson for Howell and the federal court in DC declined to comment on the nature of the recent sealed court activity, as did a spokesman for the special counsel's office.

As the court action moves forward, Trump himself has said he is working on giving information to Mueller. When asked by the Associated Press on Tuesday if he would sit for an interview with Mueller or simply answer written questions, as his lawyers have agreed to do, Trump said: "You know that's in process. It's a tremendous waste of time for the president of the United States."