A memo from the lead investigator probing misleading robocalls in the 2011 federal election reveals another instance where a Conservative Party lawyer acted as a liaison with a witness in the case.

Questions have already been raised about Arthur Hamilton's presence at interviews with witnesses who work for parliamentarians, but who weren't clients of his.

The June 7, 2013 memo from Al Mathews to the Crown prosecutor assigned to the case recounts Mathews' attempt to confirm an incident at a polling station in Guelph, Ont., the city where thousands of voters received phone calls directing them to the wrong polling station.

The memo was provided to CBC News.

"Through Arthur Hamilton, I asked questions of [Chris] Crawford," Mathews wrote about a June 16, 2012 interaction. "This was also covered in Crawford's second interview, of November, 2012."

Crawford worked for the Conservative campaign in Guelph, along with Michael Sona, the only person charged in connection with the misleading automated calls.

Hamilton sat in on interviews

Michael Sona is the only person charged with planning and executing misleading phone calls that sent voters in 2011 to the wrong polling station. (CBC) Mathews was writing the memo to provide information to Crown prosecutor Croft Michaelson in response to a request from Sona's lawyer for information about a dispute at a polling station where Sona was asked to leave after using a cellphone.

Hamilton declined to comment on whether he represented Crawford. Sona's lawyer didn't immediately respond to a request for comment. A spokesman for Elections Canada said he couldn't comment on investigations.

In testimony earlier this month at a related proceeding, Mathews said several witnesses showed up for interviews with Hamilton "in tow." He said he would have stopped the interviews immediately had any of the witnesses said they didn't want Hamilton present.

Mathews also testified that Hamilton brought three witnesses to his attention.

Five witnesses told Mathews that Sona bragged to them about arranging the calls, Mathews wrote in an affidavit released by an Ottawa court in August. A sixth witness was described as reluctant to speak.