The head of Elections Canada says elections investigators don't have the power to compel witnesses to talk, and the refusal of witnesses to provide information has delayed the robocalls investigation in Guelph, Ont.

Marc Mayrand says the inability to force witnesses to answer questions means electoral fraud cases take more time and are more complicated to investigate.

"It's a good example of a case where three people the investigator thought would have relevant information basically turned down any offer to be interviewed," Mayrand said in an interview with host Evan Solomon of CBC Radio's The House airing Saturday.

"Sometimes, they [investigations] get into a dead end for lack of co-operation from witnesses," Mayrand said.

After two years, only one person in the Guelph case has been charged, Michael Sona, and his trial won't begin until June, more than three years after the election.

On voting day during the 2011 federal election, thousands of voters in Guelph received automated calls, pretending to be from Elections Canada, directing them to the wrong polling station.

Sona was the director of communications for the failed Conservative candidate Marty Burke.

Mayrand didn't name the witnesses who refused to talk, but court documents filed by Allan Mathews, an investigator working for Canada Elections, say Andrew Prescott, the deputy campaign manager for Burke, after one phone conversation, communicated through his lawyer he would not be participating in a sit-down interview.

Mathews also relates that Sona, after speaking to him several times, did not show up to give what Mathews called "a warned statement."

Listen to CBC Radio's The House

Hear more from Chief Electoral Officer Marc Mayrand on CBC Radio's The House, Saturday at 9 a.m. (9:30 NT).

Mayrand echoed the findings of a report released Monday by the commissioner, or investigative head, of Canada Elections. Yves Côté called on the federal government to give him the power to compel people to provide information relevant to investigations.

Côté argued his office lacks investigative tools and that he needs the power to apply to a judge for an order to force witnesses to talk.

A second lengthy investigation

Mayrand referenced a second electoral fraud investigation involving another Conservative, MP Dean Del Mastro, when he  responded to a question Solomon asked about why that investigation took so long.

Solomon said Del Mastro had complained to him in interviews about the length of the investigation into his spending during the 2008 election.

In June a tearful Del Mastro told the House of Commons he had been subjected to "unfounded hatred, contempt and ridicule" due to an investigation by Elections Canada that had been going for a year.

"Electoral issues...should be addressed within one electoral cycle," Mayrand said to Solomon. "We shouldn't find out three elections down the road."

On Sept. 26,  Del Mastro was charged with overspending his 2008 campaign limit and reporting a $21,000 expense as $1,575, five years after the events allegedly occurred. He has since resigned from the Conservative caucus and will sit as an Independent when the House returns this month.

"I'm always coming back to this power to compel witnesses, which adds time to an investigation because you have to find other routes to get information," Mayrand said.

Mayrand has been asking for electoral reforms since the height of the robocalls case in 2012,

In April, the government abruptly postponed its promised electoral reform package on the day before it was supposed to be tabled in the House. A new minister of democratic reform has taken over the file, but no legislation has been forthcoming.

Mayrand said he would like to see mention of the legislation in the upcoming Speech from the Throne on Oct. 16. But, he added, the new minister, Pierre Poilievre, has indicated the reforms package will come in "late fall".

With files from Karina Roman