Manafort has reportedly visited Mueller's office 9 times over the last month, for hours at a time

• Paul Manafort has reportedly visited the special counsel Robert Mueller's office at least nine times over the last month.
• Once there, he and his lawyers are said to have spent at least six hours at a time with prosecutors.
• Manafort is Mueller's most significant cooperating witness to date, and his frequent trips to Mueller's office indicate the Russia investigation is not slowing down any time soon.

Paul Manafort has visited the special counsel Robert Mueller's office at least nine times over the past month, for hours at a time, CNN reported.

A black SUV carrying Manafort has reportedly been seen arriving at Mueller's office around 10 a.m. ET several times since September. Manafort's lawyers are said to arrive at the same time, and they all spend around six hours inside the special counsel's office at a time.

Manafort pleaded guilty in September to two counts of conspiracy and obstruction as part of the ongoing Russia investigation.

He is arguably Mueller's most significant cooperating witness to date, given his role leading President Donald Trump's campaign during the most pivotal period in the 2016 election.

Manafort was the chairman of the Trump campaign when he offered a Russian oligarch "private briefings" on Trump's bid. He was one of three top Trump campaign officials to attend a meeting with two Russian lobbyists offering dirt on Democratic nominee Hillary Clinton at the height of the campaign.

And he was leading the campaign when the radical pro-transparency group WikiLeaks began dumping thousands of emails from the Democratic National Committee that had been stolen by Russian operatives.

His cooperation with the special counsel comes amid heightened calls from the president's allies for Mueller to wrap up the Russia investigation.

Mueller has not given any public indication that he will do so. But two US officials told Bloomberg this week that the special counsel is close to getting answers to the two core questions in the investigation: whether members of the Trump campaign colluded with Moscow to sway the 2016 race in his favor, and whether Trump sought to obstruct justice after the existence of the Russia probe became public knowledge.

News out of Mueller's office has been slow over the last few weeks as the November 6 midterm election approaches, a sign that prosecutors are adhering to DOJ guidelines that warn against taking any overt actions that can be seen as influencing the outcome of an election.

But Manafort's frequent trips to Mueller's office indicate the investigation is doing anything but slowing down.

On Wednesday, ABC News reported that Mueller's prosecutors have been grilling Manafort for information on the longtime GOP strategist Roger Stone. Stone told Business Insider he didn't do anything wrong but expects to be charged soon because he believes he is being "framed."

Legal experts say they expect to see a string of new revelations from Mueller's office once the election is over, but that they don't anticipate the special counsel releasing a final report of his findings any time soon.

What he may do, they added, is release a report of his findings in the obstruction inquiry, which he is reportedly close to wrapping up.

Meanwhile, Trump's team is currently in the middle of providing written answers to the special counsel on questions focusing on potential collusion with Russia. Mueller has reportedly made clear that he wants to ask follow-ups as well, and prosecutors have not ruled out a one-on-one sit-down with the president.

Jed Shugerman, a professor at Fordham Law School, said he believes it is significant that Mueller agreed to narrow the scope of his initial questions for Trump to focus on collusion rather than obstruction.

"It suggests Mueller thinks that's more significant and worthwhile at this stage," he said.

Shugerman added that Mueller's questions about collusion indicate that "he probably has sufficient evidence for obstruction. If forced to allocate his time to obstruction or Russia, he is choosing Russia. And probably [because] he has big leads."