A top political adviser to former Ontario premier Dalton McGuinty was found guilty Friday of criminal charges for wiping government computers following the cancellation of two gas-fired power plants.

David Livingston, who was McGuinty's chief of staff in 2012-13, was found guilty on one charge of unauthorized use of a computer and one charge of attempting to commit mischief to data.

The Crown is seeking jail time and it's a decision that Brian Gover, Livingston's lawyer says is a step too far.

"We consider that to be an absurd position given Mr. Livingston's outstanding good character," Gover said.

Meanwhile, Livingston's deputy, Laura Miller, was found not guilty on the same charges.

"She's gratified to be able to move on with her life," said Scott Hutchison, Miller's lawyer.

"She and her family have found this to be an incredibly difficult time and they're glad to have that behind them," Hutchison said.

The ruling is a dramatic twist in a controversy that has swirled around Ontario politics for the past seven years: the costly cancellation of two gas-fired power plants in Mississauga and Oakville.

The charges against Livingston and Miller were laid over allegations the pair ordered the wiping of computers in the premier's office in early 2013, just before McGuinty's administration gave way to that of fellow Liberal Premier Kathleen Wynne.

The verdict against Livingston could play into the upcoming provincial election in June as opposition parties try to place blame.

"The fact that you've got a most senior staffer of a premier convicted now is proof positive that there's an absolute rot of corruption through the Liberal party," said Victor Fedeli, PC MPP for Nipissing.

"We have a sense of a Liberal government, a Liberal party that will do anything at any price to families to protect its seats, to protect itself and that was just validated by the guilty verdict today," said Peter Tabuns, NDP MPP for Toronto-Danforth

Livingston arrives at court in Toronto on Sept. 11, 2017. (Colin Perkel/Canadian Press)

Though Miller was ultimately found not guilty, Justice Timothy Lipson eviscerated her and Livingston's defence case in his lengthy judgment, calling some of their explanations "implausible" and characterizing their tactics as "dishonest."

Lipson said the evidence suggested Livingston was "rather more interested in deleting emails" than in ensuring relevant government documents were retained.

He said there was "compelling circumstantial evidence" that both Livingston and Miller believed there were files on the computers that ought to have been retained.

But he said the evidence did not prove beyond a reasonable doubt that Miller intended to wipe such data from the hard drives.

Livingston's sentencing hearing is scheduled for Feb. 26, shortly after the Ontario Legislature resumes its final sitting before the election campaign.

Case hinged on intent

Prior to issuing the verdicts, Lipson said that the case turned on whether the Crown could prove beyond a reasonable doubt that Livingston and Miller ordered the computers wiped with the intent to delete data that they had an obligation to retain.

He said there was "no dispute" that the two accused enlisted Miller's common-law spouse Peter Faist to wipe 20 computers in the premier's office. The judge also said it was clear from the evidence that Livingston obtained a special administrative password to allow Faist to do so.

Faist is an IT consultant who was not part of the Ontario public service. He is not charged but did testify in the trial. The Liberal caucus, not the government, paid him about $10,000 for the work.

Miller arrives at court in Toronto on Sept. 11, 2017. (Colin Perkel/Canadian Press)

The Ontario Court of Justice trial began at Toronto's Old City Hall courthouse in September. Since then, the Crown's case was gradually whittled away.

First, the Crown's computer forensics specialist was disqualified from testifying as an expert witness because the judge ruled he was too deeply involved with the police during the investigation. It meant the Crown could not present any evidence about what documents were actually destroyed.

Then, as the Crown wrapped its case, it dropped a charge of breach of trust against the two accused.

Finally, the judge downgraded a mischief charge to attempted mischief.

The Ontario PCs have used the trial as part of recent attack ads against the Wynne government, calling the Ontario Liberals politically corrupt. Friday's ruling, coupled with last fall's acquittal of two other Ontario Liberals who had faced bribery charges in an unrelated case, could force the PCs to change their tactics.

Federal Crown lawyers prosecuted the case against Livingston and Miller. They were brought in by Ontario's attorney general to prevent any perception of conflict of interest.

Defence lawyers failed in an earlier motion during the trial to have the charges tossed for lack of evidence, arguing the Crown's case was circumstantial.