Sona, who handled media relations for the 2011 Conservative campaign for Marty Burke, has been charged with wilfully preventing or trying to prevent a voter from casting a ballot.
The 25-year-old remains the only person charged following an investigation into allegedly misleading phone calls that went out in the riding of Guelph, Ont., during the federal election in 2011.
In an affidavit filed in court on Oct. 24, Allan Mathews, the investigator for the office of the commissioner of Canada elections, said the publicity surrounding the high-profile case is having a "chilling effect" on the witnesses.
While the names of the witnesses are subject to a temporary publication ban, Mathews described the witnesses as "employed by or through a political party" and as "junior political staff."
Two witnesses "expressed concerns that having any publicized involvement with the 'robocalls' could risk their employment," Mathews said in the sworn affidavit.
The sworn affidavit by Mathews comes in response to a request by the CBC, the Ottawa Citizen and Global News to have a publication ban lifted on a previous document that laid out evidence against Sona. The media outlets are challenging the ban at a hearing on Nov. 13.
Witness harassment and reluctance to co-operate
On Wednesday, Crown prosecutor James Clark filed a statement of facts warning that not only is there "evidence that harassment of witnesses is already occurring" but "Mr. Sona himself has demonstrated that he will attack these witnesses personally, persistently, and publicly once their names can be published."
The witnesses in question are the ones who have provided "the most prejudicial evidence against Mr. Sona," the Crown prosecutor said.
Clark warned that Sona has begun to make "negative comments on social media regarding the yet unnamed witnesses, stating that they have 'credibility problems' and implying that they have lied and misled investigators in order to secure promotions."
One key witness told Mathews, the investigator, that "fear" of causing a politically embarrassing situation for the minister he worked for was one of the reasons why he did not come forward sooner with information.
"You let your fear run with you and then that would be embarrassing for the minister. I would say that was also a huge primary fear of mine," the witness told Mathews.
The lead investigator said the first witness also reported receiving a Facebook message from an acquaintance of Sona's accusing him of being a liar and calling into question his character as a result of his co-operation with the Elections Canada investigation.
Mathews said the distant acquaintance has approached him in the past on the basis of knowing Sona.
Sona or his lawyer were not immediately available for comment.
Temporary publication ban upheld
The Crown prosecutor, in his statement of facts, warned against the publication of the witnesses' names, saying that it would "increase witness reluctance to participate in this case and similar cases forward, and will inevitably lead to persistent harassment of these witnesses."
For that reason, Clark said, there is no harm in delaying the publication of the witnesses' names until the trial.
Mathews, the lead investigator, said a second witness was "very reluctant" to provide him with information and did so only because the first witness had involved him in the investigation.
The first witness quoted the second witness as saying that he would "probably have a hard time finding a job after … because nobody likes the media attention."
Mathews said he attempted to interview approximately 11 people who worked on Burke's election campaign team but most did not co-operate.
One worker who Mathews said was "directly involved" with access and use of the party's database "flatly refused to co-operate" for fear of having his name made public.
Mathews said he heard that same concern from "several" other workers. Two others declined to co-operate without giving Mathews any specific reason.
In the affidavit, Mathews said the one worker who agreed to co-operate told him that she has altered her C.V. to avoid any link to the Burke campaign on which she worked, "for fear of the negative impact" of being associated with the robocalls.
Sona is due in court for a pre-trial or a trial on June 2, 2014.