Conservative Party lawyer Arthur Hamilton directed an Elections Canada investigator to three witnesses in the agency's robocalls probe, an Ontario court heard Wednesday.

It's the latest reference in a series of cases to the lawyer who represents the country's governing party.

Hamilton was named by now-suspended Senator Mike Duffy as one of a number of party officials who allegedly helped broker a deal to repay his $90,000 in questionable Senate expenses.

Hamilton also defended six MPs in a Federal Court challenge over a pattern of misleading robocalls outside of Guelph, and accompanied witnesses to their interviews with Elections Canada in the investigation of the robocalls that took place in Guelph, Ont., in the last federal election.

Al Mathews, who's leading the election agency's probe into those misleading robocalls in Guelph, said he didn't know about three of the witnesses until Hamilton approached him and said he'd want to speak to them.

The witnesses' names are covered under a publication ban. CBC News is challenging the ban along with several other media outlets. Mathews was testifying as part of that challenge.

It's the first time Mathews has made public comments about his investigation, which dates back to days after the May 2, 2011 federal election.

Michael Sona, 25, is the only person facing charges over the automated calls, which allegedly directed hundreds of voters to the wrong polling station. Sona is also in court to observe the proceedings.

Hamilton brought witnesses to Mathews

The witnesses told Mathews, according to an affidavit he filed in court, that Sona told them about the robocalls.

All of them have connections to the federal Conservatives, with some employed by Parliamentarians.

Under cross-examination by Richard Dearden, the lawyer representing the media, Mathews said Hamilton phoned him to tell him about three of the witnesses in 2012.

"He thought [they] would have information relevant to my investigation," Mathews said.

Michael Sona

Michael Sona, 25, is the only person facing charges over the so-called robocalls affair, when hundreds of voters were allegedly directed to the wrong polling station during the last federal election campaign in 2011. (CBC)

Hamilton also sat in on several of the interviews, Mathews said, even though he identified himself as counsel to the party and not to the witnesses.

Mathews said none of the witnesses told him that they didn't want Hamilton in the interviews, or he would have stopped the interviews "immediately."

"I understood they were essentially employees of the party," Mathews said, or that their employment was "a gift of the party."

Asked why he let Hamilton accompany the witnesses into the interview, Mathews said the lawyer showed up with them.

"Because they presented themselves with him in tow," he said.

MP directed witness to party

But the staffers weren't directly employed by the party, Dearden said, in an exchange with Mathews.

"They're not technically employees of the party... no, they're not employees of the party, you're right," Mathews conceded.

One witness had concerns about what Sona allegedly told her, Mathews said, and told the MP for whom she worked.

That MP, Mathews said, directed her to Conservative Party director of communications Fred Delorey, who then directed her to Hamilton.

"Anything that had a Conservative Party imprint on it, Mr. Hamilton was involved," Dearden said.

Sona's lawyer requested a publication ban on Aug. 26 on the information provided by the witnesses, which was included in an affidavit filed by Mathews in order to get a production order,

The ban has already been varied twice to allow publication of some information. The only remaining ban covers the names of the witnesses.

Judge Célynne Dorval will rule Friday at 10 a.m. on whether to fully lift the ban.