Green Party Leader Elizabeth May says it's time to reopen investigations into alleged robocalls made by Conservatives - in light of recent testimony by Sen. Mike Duffy.

May said in a newly-released letter that no one challenged Duffy's statements in court, during his recent trial, about a Conservative "black ops group" that broke the rules during the 2008 election. As a result, she said investigators must look into the matter.

"It is alarming to me and to many of my constituents that voter fraud may have been committed in our riding and no one has been caught," wrote May in her letter, dated May 31.

It was sent to Elections Canada CEO Marc Mayrand and other federal officials, including the commissioner of Canada Elections, Yves Coté.

Duffy, who was facing a range of charges including bribery, fraud and breach of trust - but ultimately found not guilty, testified last December that former Conservative cabinet minister Gary Lunn had been helped, though he didn't know it, by a "black ops group" in the Conservative party, headed by the party's campaign director Doug Finely. Duffy went on to say that robocalls had been used to mislead and split NDP voters to facilitate a Conservative victory.

He said that Lunn had “had a close call during the previous election and it was only through the divine intervention of Doug Finley's black ops group at Conservative headquarters that he managed to get himself re-elected.”

May's spokesman Daniel Palmer said an investigation should be launched immediately.

"Now that Duffy's [trial] wrapped up, we feel the time is right," said Palmer.

The only person to be convicted in connection with illegal robocalls was former Conservative staffer Michael Sona, who recently lost a bid to appeal a nine-month sentence.

Elections Canada said that any investigation would have to come from the office of the commissioner of Canada Elections.

A spokeswoman for the commissioner stated that it hadn't yet received May's letter, but she said that its investigation into robocalls had already concluded.

"We’re aware of what Mr. Duffy said. If there is new information that comes to light, we’ll look into it. But we do not divulge the nature of our investigations," said the spokeswoman.

This isn't the first time that May has called for the investigation to be reopened. In December 2015 May, along with 2008 Liberal candidate Briony Penn and a federal NDP official, called for a reopening of the investigation as soon as Duffy's testimony was made public.

“The tricks that were tested in 2008 were put to use again in 2011,” May said in a statement. “While one individual has been convicted, all parties responsible for thousands of fraudulent phone calls – each one of them a criminal offense under our elections law – remain at large."