Washington (CNN) Roger Stone's allies are springing to his defense -- in front of a grand jury -- as special counsel Robert Mueller's team continues its investigation into Stone.

Two of Stone's associates, filmmaker David Lugo and attorney Tyler Nixon, said they have testified in recent weeks in front of Mueller's grand jury. In interviews with CNN and other media outlets, both men have said they witnessed New York radio host and political activist Randy Credico refer to himself as Stone's intermediary to WikiLeaks.

Stone, a longtime adviser to President Donald Trump, has been under scrutiny over whether he had advance knowledge that WikiLeaks would release hacked material during the 2016 presidential campaign and whether he shared any of that material with members of the Trump campaign. Roughly a dozen of Stone's current and former associates have been contacted by Mueller's team for interviews or to testify before the grand jury. An attorney for Stone said Stone still has not been contacted.

As investigators have examined Stone's potential contact with WikiLeaks, they've faced conflicting accounts. After proclaiming he was in touch with WikiLeaks founder Julian Assange in 2016, Stone amended his story to say he actually used a back channel: Credico. Credico has denied that he acted as a go-between.

Lugo and Nixon took to the pages of The Washington Post last month to bolster Stone's version of events, saying that Credico acknowledged being the source of Stone's election year proclamations about WikiLeaks.

It appears that Mueller's investigators decided to follow up.

Both Nixon and Lugo were questioned about whether there was an effort to intimidate Credico -- a charge both men denied. They also offered testimony that could reinforce Stone's claim that Credico served as his intermediary.

Credico has said he was speaking sardonically when he referred to himself as a back channel because he knew Stone was referring to him as such.

"It changes nothing," Martin Stolar, Credico's attorney said of the testimony from Lugo and Nixon. "Randy's statements that he's publicly made before are statements that he stands by."

"Mr. Stone has spoken truthfully on this matter from day one," said Grant Smith, an attorney for Stone. "Yet everyone was assigning greater credibility to Mr. Credico than to Mr. Stone. For reasons known to Mr. Credico... it has been Mr. Credico who was attempting to downplay his involvement."

Lugo told CNN that he appeared before the grand jury for about half an hour and handed over copies of his communications with Credico.

He said he recounted for the grand jury an interaction with Credico in May 2017. At the time, Credico was helping Lugo arrange an interview with Stone, Lugo said. During the encounter, Lugo said Credico seemed out of sorts.

"He said the heat was on," Lugo said. "He said. 'I'm the one who connected Roger with the WikiLeaks stuff.'"

In one message, Credico wrote, "I knew Rodger (sic) was going to name me sooner or later and so I told you that I'm the so-called back Channel," according to a copy of the message provided by Lugo.

As part of the investigation into Stone, Mueller's team has obtained copies of seemingly threatening messages that Stone has sent to Credico, who has participated in multiple interviews with Mueller's team and testified before the grand jury. Stone said he was not trying to intimidate Credico

When Lugo was asked about whether there was some kind of harassment campaign targeting Credico, he said Credico was the one sending the menacing messages.

"I've never tried intimidating Randy — ever," Lugo told CNN. "He's trying to intimidate me."

Lugo said he handed over months of "threatening" messages from Credico, which he believes were an effort to keep him quiet after Credico acknowledged his backchannel role in Lugo's presence.

In one series of messages that Lugo shared with CNN, Credico said he planned to talk about Lugo on an upcoming podcast, adding, "I'm going to bury you champ."

In the messages, Lugo said he was prepared to sue Credico for defaming him and his business.

In an interview with the right-wing Daily Caller , Nixon said he was asked whether Stone ever tried to intimidate Credico. He said he never witnessed an intimidation effort.

Nixon didn't respond to CNN's request for comment. But in the Daily Caller interview, he recounted a dinner that he, Credico and Stone had in New York in November 2017. The dinner came after Stone told the House Intelligence Committee that Credico was his back channel to WikiLeaks.

"It was clear from the conversation," Nixon told the Daily Caller, that "Stone had not invented this or thrown Credico in this as a decoy."

Nixon told the grand jury that Credico appeared upset that he would be revealed as Stone's source because it might upset Credico's left-leaning friends.

By Nixon's recollection, Credico said at the time: "I can't admit this. I can't say this."