Special counsel Robert Mueller's team has presented witnesses with some of Roger Stone's emails and text messages during their interviews for the Russia investigation.

Stone did not hand the materials over to the special counsel's office or Congress, CNN reported Tuesday, and it's unclear how investigators obtained them.

Witnesses have also been asked about Stone's "dirty trickster public persona," sources told CNN.

Investigators are interested in what Stone did in 2016 when he was a confidant of then-candidate Donald Trump, including his communications with WikiLeaks and a group of hackers linked to Russian intelligence. The hackers were indicted by Mueller for their alleged electronic incursion into Democratic National Committee and Democratic Congressional Campaign Committee email accounts.

Stone, who was a political aide to former President Richard Nixon, has denied collaborating with WikiLeaks founder Julian Assange to coordinate the release of information damaging to Trump's then-opponent Hillary Clinton.

Stone reportedly piqued the interest of Mueller's team after he appeared to foreshadow the WikiLeaks dump of John Podesta's emails when Podesta was Clinton's campaign chairman. The drop coincided with the October 2016 publication of the "Access Hollywood" tape in which Trump was recorded bragging about sexual assault.

Although a number of Stone's associates have been questioned by Mueller's office, he says he has not been contacted by the special counsel.

Stone told CNN on Tuesday he had "always acknowledged playing hard-ball politics," but his "tactics do not include breaking the law."

"This would not be the first time the special counsel has willfully misled the grand jury," Stone added.

Stone told the Washington Examiner his lawyers suspect Mueller's office "engaged in 'parallel construction' to access emails or text messages originally obtained illegally and unconstitutionally."

"Parallel construction" is where federal officials conceal intelligence and law enforcement sources and methods by offering another explanation for how agents got that information, according to Human Rights Watch.

"Having come up empty-handed of any proof of Russian collusion, Wikileaks collaboration or advance knowledge of the acquisition and publication of John Podesta's emails any effort by Mueller to frame me for some other bogus offense will bring these issues to light," Stone said via email.