Sona faces a single charge of wilfully preventing or endeavouring to prevent a voter from casting a ballot, in the so-called robocalls case related to automated calls made with a phone registered under the pseudonym Pierre Poutine on election day – May 2, 2011.
On Tuesday, Sona's lawyer suggested Prescott may be the real culprit behind the call.
Prescott has rarely spoken about the robocalls investigation, but in October 2012 called misleading voters a "disgusting" trick and said he appreciated the support of family and friends who knew he had nothing to do with it.
Prescott's immunity agreement may make him the most important witness in the Crown's case.
The IT worker, who left Ontario in the wake of the allegations swirling around the Guelph Conservatives in the past few years, was supposed to testify Tuesday, but extended questioning of another witness delayed his first public comments in a year and a half.
Prescott arrived alone at the courthouse Tuesday afternoon and had to pass Sona, who gave him a tight smile. The two haven't spoken in months despite having toiled on the same election campaign.
Earlier in the day, Sona's lawyer, Norm Boxall, questioned other witnesses about whether Prescott could have made the misleading calls.
Sona has always said he had nothing to do with the calls, but faces up to five years in prison if convicted of the single charge.
Sona, 22 at the time of the campaign, was the director of communications for Conservative candidate Marty Burke.
Burke's campaign manager, Ken Morgan, moved to Kuwait in the months after the election and isn't expected to be back in Guelph to testify.
While hundreds of people outside Guelph also complained about misleading or harassing robocalls, a report by Elections Canada later found that there wasn't enough evidence to support the idea of a co-ordinated campaign to suppress the vote across the country.
The trial, which began Monday, is to last eight days.