Photo: CTV

Protesters take part in a robocall protest on Parliament Hills in Ottawa on Monday, March 5, 2012. (Sean Kilpatrick /THE CANADIAN PRESS)

Canada's elections investigator says there is not enough evidence concerning fraudulent robocalls during the 2011 election to warrant charges by the federal public prosecutor.

The long-awaited report from commissioner of elections Yves Cote lays out what he calls the difficulties that investigators faced in gathering evidence in ridings other than Guelph, Ont., where a single junior Conservative staffer faces charges.

Cote says as a result, he won't be referring the matter to the federal director of public prosecutions -- a conclusion that he says is supported by an independent review by a former Supreme Court justice.

Cote's investigation is separate from robocall allegations during the same election in Guelph, where Michael Sona faces Elections Act charges for his alleged role in calls that impersonated Elections Canada.

The report says the time it took many Canadians to report the calls complicated the investigation as memories faded, and potential witnesses and parties also did not fully co-operate with investigators.

Cote says Elections Canada needs the power to compel testimony -- something the Conservative government left out of its controversial new elections overhaul despite calls last year for increased investigative powers.