Police probing the destruction of documents in former premier Dalton McGuinty's office are ramping up the investigation, serving Queen's Park staff with a production order for records.

What's more, Ontario Provincial Police confirmed they have interviewed Mr. McGuinty as part of the probe, which relates to the billion-dollar cancellation of two gas-fired power plants to save Liberal seats in the 2011 election.

The development thrusts the scandal back into the spotlight just a week before the current election, in which Mr. McGuinty's successor is locked in a tight race to preserve the Liberals' rule in the province.

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On Thursday, before the latest developments came to light, Liberal Leader Kathleen Wynne apologized for the scandal in a meeting with The Globe and Mail's editorial board, offering a frank admission that the cancellations were done for political gain.

"I am very sorry about the way it happened," she said. "I'm mostly sorry because I really believe that partisan interests were placed above the public good, and that's not why I got into politics."

Ms. Wynne was not involved in the cancellation decision or alleged to have been part of any destruction of documents, but has had to deal with the political fallout since she took office early last year.

The officers are investigating allegations Mr. McGuinty's staff deleted e-mails and other documents that may have shed light on the former premier's decision to cancel the plants. The investigation has zeroed in on David Livingston, Mr. McGuinty's last chief of staff. Police believe he let an outside IT consultant – the partner of another McGuinty official – into the office to erase records. Police say allowing a non-government worker access to government computers could be a breach of trust. Neither the IT consultant nor his partner are under investigation.

OPP Sergeant Pierre Chamberland said on Thursday that the force was seeking documents from the legislature.

"I can confirm that the OPP obtained a Production Order from Court in Ottawa for certain documents in relation to this ongoing investigation which it served on employees of the Ontario Legislature," he wrote in an e-mail. "Mr. McGuinty was interviewed by the investigative team in April."

The former premier has said he did not order, take part in or have any knowledge of the destruction of records.

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Mr. Livingston has also maintained his innocence. His lawyer has called the allegations against him "baseless."

As a cabinet minister under Mr. McGuinty, Ms. Wynne signed an order allowing the government to negotiate with the firm building one of the plants. She told The Globe that if she had known at the time how it would turn out, she would not have signed it.

"If I had all the information I have now, then, would I have behaved differently? Absolutely," she said.

The gas plants scandal has haunted Ms. Wynne. In this week's debate, she was asked repeatedly why she signed the negotiating mandate.