Special counsel Robert Mueller's team is asking witnesses pointed questions about whether Donald Trump was aware that Democratic emails had been stolen before that was publicly known, and whether he was involved in their strategic release, according to multiple people familiar with the probe.

Mueller's investigators have asked witnesses whether Trump was aware of plans for WikiLeaks to publish the emails. They have also asked about the relationship between GOP operative Roger Stone and WikiLeaks founder Julian Assange, and why Trump took policy positions favorable to Russia.

The line of questioning suggests the special counsel, who is tasked with examining whether there was collusion between the Trump campaign and Russia during the 2016 election, is looking into possible coordination between WikiLeaks and Trump associates in disseminating the emails, which U.S. intelligence officials say were stolen by Russia.

Trump has repeatedly denied any collusion and has described the special counsel's investigation as "illegal" and a "witch hunt."

“Russians had no compromising information on Donald Trump” @FoxNews Of course not, because there is none, and never was. This whole Witch Hunt is an illegal disgrace...and Obama did nothing about Russia! — Donald J. Trump (@realDonaldTrump) February 24, 2018

In one line of questioning, investigators have focused on Trump's public comments in July 2016 asking Russia to find emails that were deleted by his then-opponent Hillary Clinton from a private server she maintained while secretary of state. The comments came at a news conference on July 27, 2016, just days after WikiLeaks began publishing the Democratic National Committee emails. "Russia, if you're listening, I hope you're able to find the 30,000 emails that are missing," Trump said.

Witnesses have been asked whether Trump himself knew then that Clinton's campaign chairman John Podesta, whose emails were released several months later, had already been targeted. They were also asked if Trump was advised to make the statement about Clinton's emails from someone outside his campaign, and if the witnesses had reason to believe Trump tried to coordinate the release of the DNC emails to do the most damage to Clinton, the people familiar with the matter said.

The White House spokesman at the time, Sean Spicer, would later say that then-candidate Trump had been "joking" when he called on Russia to hack his opponent's emails.

"In 2016, the hack of my emails was often treated as a politically interesting event," said Podesta to NBC News via email. "For the record, it was a crime. Glad Mueller is trying to get to the bottom of everyone involved in that crime."

What did Stone know?

Investigators are also asking questions about Trump's longtime relationship with Stone, the Republican operative, according to witnesses. Investigators have asked about Stone's contacts with WikiLeaks during the campaign and if he's ever met with Assange.

"They wanted to see if there was a scheme. Was Stone working on the side for Trump?" after he officially left the campaign, one person interviewed by the special counsel's office said, adding that it seemed investigators wanted to know, "Was this a big plot?"

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

Russia stole emails from the DNC and Podesta, according to U.S. intelligence officials, and released batches of them through WikiLeaks starting in July 2016 and up until the election.

Click here to see NBC's interactive Russia timeline

As part of his plea agreement with the special counsel, former Trump foreign policy adviser George Papadopoulos revealed that in a conversation in late April 2016, he was told by a professor with ties to Russian officials that they had "dirt' on Clinton in the form of "thousands of emails." A 10-page memo from Democrats on the House Intelligence Committee released Saturday noted that the Justice Department's October 2016 application for a FISA warrant on another Trump foreign policy adviser, Carter Page, included the fact that Russian agents had previewed their hack and dissemination of stolen emails to Papadopoulos.

Investigators were interested in statements Stone made in the final month of the 2016 campaign that strongly suggested he was aware of information the group had before it became public and when it might be released. In one instance, he wrote on Twitter that "it would soon be Podesta's time in the barrel." Weeks later Podesta's stolen emails were released by WikiLeaks.

As WikiLeaks was strategically publishing stolen emails in the closing months of the campaign, Trump also publicly said he loved the group. He mentioned WikiLeaks 145 times during the last month of the 2016 campaign. In 2017, President Trump's CIA director, Mike Pompeo, would label the group a hostile non-state actor.

Investigators also have shown interest in any connections Stone has to WikiLeaks and Assange, its founder. Stone has said he communicated with Assange and WikiLeaks through an intermediary he described as a journalist.

The Atlantic reported this week that Stone exchanged direct messages on Twitter with WikiLeaks. Rep. Adam Schiff of California, the top Democrat on the House Intelligence Committee, has said his committee should subpoena Twitter to produce any direct messages "from and between the Twitter handles identified as relevant to the Russia investigation," including WikiLeaks, Assange and Stone. According to Schiff, Twitter has told the committee it won't produce such messages "absent compulsion."

Mueller's team has asked witnesses if Stone ever met with Assange. Stone has denied ever communicating directly with Assange.

Stone served briefly on the Trump campaign in 2015, leaving in August of that year. At the time he said he quit, while the campaign said he was fired.

Investigators have asked witnesses about Stone's time on the campaign and what his relationship was like with Trump after he left.

"How often did they talk? Who really fired him? Was he really fired?" a witness said, describing the line of questioning.

In a statement, Stone said he had "no advance knowledge of the content or source of information published by WikiLeaks."

"I have not been interviewed by the special counsel," wrote Stone. "I never discussed WikiLeaks, Assange or the Hillary disclosures with candidate Trump, before during or after the election. I have no idea what he knew about them, from who or when. I have never met Assange."

Stone appeared before the House Intelligence Committee for four hours last September. In his prepared opening statement, which he also delivered publicly on the InfoWars YouTube channel, Stone denied that he ever engaged "in any illegal activities on behalf of my clients, or the causes which I support." He denied having direct contact with Assange and called any exchanges with Guccifer 2.0, which took credit for hacking the DNC, "innocuous."

And he said his tweet predicting that Podesta would spend time in the "barrel" was in the context of the coverage of the resignation of former Trump campaign chair Paul Manafort, whom he called his "boyhood friend and colleague," over allegations about business activities in Ukraine.

Trump's policy positions

At that same July 2016 news conference where he referenced Clinton's missing emails, candidate Trump said he was open to lifting sanctions on Russia and possibly recognizing its annexation of Crimea in Ukraine. The U.S. and its European allies had sanctioned Russia because of its intervention in Ukraine and annexation of Crimea, which the Obama administration refused to recognize.

Investigators have asked witnesses why Trump took policy positions that were friendly toward Russia and spoke positively about Russian President Vladimir Putin, according to people familiar with the probe.

Investigators have also inquired whether Trump met with Putin before becoming president, including if a meeting took place during Trump's 2013 visit to Moscow for his Miss Universe pageant. Trump has given conflicting responses on when he first met Putin.

At least one witness was asked about Trump's business interests in Moscow and surmised afterward that the special counsel investigation may be focused on business dealings that took place during the campaign.

Witnesses also have been asked about Stone's connections to Manafort.

At least one witness has been asked about Trump aide Dan Scavino, specifically about any involvement he may have had in the campaign's data operation. Scavino currently runs the White House's social media operations and is one of Trump's closest aides.

NBC News reached out to Trump's legal team and the White House. The White House declined to comment on Scavino "out of respect for the Office of Special Counsel and its process. ... The White House remains fully cooperative with the Office of Special Counsel and we look forward to [the investigation's] prompt conclusion."

John Dowd, the president’s outside attorney, told NBC News, "We do not discuss our knowledge of or communications with the special counsel."

Peter Carr, a spokesman for Mueller, declined to comment.