The Ontario Provincial Police launched a criminal investigation Friday into the destruction of emails about the costly cancellation of two gas plants by senior Liberal staff.

The Criminal Investigation Services will probe Tory complaints about "alleged impropriety" by former top staffers, said OPP Commissioner Chris Lewis.

"We're conducting a criminal investigation, so if there's no criminal charges, we'll be out of there," he said in an interview late Friday.

"If a criminal act did occur, then we'll try to prove who did it and lay charges accordingly."

The probe comes in the wake of a scathing report by the province's privacy watchdog that found top Liberals broke the law by deleting emails on the cancelled gas plants in Oakville and Mississauga.

Information and Privacy Commissioner Ann Cavoukian reported Wednesday that David Livingston, former premier Dalton McGuinty's chief of staff, tried as late as January to find out how to permanently delete emails related to the gas plants.

The opposition parties say the emails were wiped out to try to cover up the true costs of cancelling the gas plants, which has grown to an estimated $585 million, well above the $230 million the government had claimed.

The first step will be for police to interview the people who made the allegations and then those who are named, Lewis said. But it's hard to say how long it may take before police determine whether any criminal charges should be laid.

"Our officers will follow the evidence and go as far as they need to either prove or disprove that something occurred," he said.

The OPP launched a criminal probe into financial irregularities at Ontario's Ornge air ambulance service over a year ago, with no charges laid, Lewis said.

"When you start trying to retrieve data and conduct interviews, sometimes it takes much longer that what we see on TV when they wrap it all up in an hour and a half."

Premier Kathleen Wynne, who won the leadership contest in late January, has said that she'd co-operate with any investigation.

She also said that the mass email deletions were unacceptable and staff have been made aware of their record retention obligations.

The New Democrats are pushing for McGuinty to appear again before the legislative committee that's looking into the cancelled gas plants, saying he needs to explain the deleted emails.

"Dalton McGuinty needs to come back and answer this new information from the privacy commissioner," said NDP energy critic Peter Tabuns.

The committee needs to know whether McGuinty told Livingston to ask for information about destroying all the records on the computers, he said.

"On the other hand, did (McGuinty) in fact make it clear to him that information had to be preserved and the law followed?"

In addition to McGuinty and Livingston, the NDP also want to hear from several other senior Liberals whose email accounts were deleted, including Craig MacLennan, the former chief of staff to the minister of energy.

McGuinty left the premier's office in late January, but remains the MPP for Ottawa South. His office said Friday that he was not available to comment, and declined to answer questions on whether or not he would agree to testify about the deleted emails.

Sitting members can't be compelled to testify at committee, but Tabuns said he expects Wynne to force the former premier to show up.

"Kathleen Wynne has made it very clear that if people have questions about those emails with regard to the former premier, he should be asked," said Tabuns. "She should make sure that that member of her caucus appears and answers questions."

In a statement released later Friday afternoon McGuinty said "at no time did he condone or direct the deletion of public documents which ought to have been preserved."

McGuinty also said in the statement he encouraged the current government to "devote all necessary resources" to training staff in "their record management obligations."