Two senior staffers in former Ontario premier Dalton McGuinty's office went to "extraordinary lengths" to "indiscriminately" wipe the contents of government hard drives to ensure no records existed in connection with the cancellation of two gas-fired power plants, a criminal trial has heard.

"It defies common sense and logic to suggest that this 'nuclear' approach was aimed at deleting personal photographs, medical records, résumés and similar documents," prosecution lawyer Tom Lemon said in his closing arguments on Wednesday.

Mr. Lemon said the actions of David Livingston, chief of staff in the premier's office, and Laura Miller, deputy chief of staff, must be viewed against the backdrop of a political controversy over the government's failure to produce records related to its decision to pull the plug on the two power plants in the months leading up to Mr. McGuinty's resignation.

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Lawyers for the two accused countered in their closing arguments that the Crown has not presented "a shred of evidence" that Mr. Livingston and Ms. Miller knew wiping the hard drives would result in the deletion of government records they were required to retain.

"All the Crown can do is link the controversy over the cancellation of the gas plants to the cleaning of the computers," Brian Gover, a lawyer for Mr. Livingston said. The Crown "never got anywhere close to the extremely high bar of proving guilt beyond a reasonable doubt."

The closing arguments followed nearly four weeks of testimony in a courtroom in Toronto's Old City Hall. Justice Timothy Lipson of the Ontario Court of Justice will hand down his decision on Jan. 19.

Mr. Livingston and Ms. Miller were initially accused of destroying e-mails and other government records related to the cancellation of the power plants. But Mr. Lemon asked Justice Lipson earlier this month to drop breach of trust charges against the two, saying the Crown cannot prove that specific e-mails were deleted.

Defence lawyers had sought a directed-verdict of acquittal on two remaining charges: mischief and unauthorized use of a computer in connection with the wiping of 20 hard drives in the premier's office. Mr. Livingston and Ms. Miller have each pleaded not guilty.

Justice Lipson reduced the mischief charges against the two to attempted mischief.

Police allege that Mr. Livingston hired Peter Faist, a non-government IT expert and the spouse of Ms. Miller, to "wipe clean" the computer hard drives just days before Mr. McGuinty resigned in February, 2013.

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Mr. Lemon said on Wednesday that Mr. Faist was not asked wipe the hard drives for every computer in the premier's office. Rather, he said, Mr. Livingston and Ms. Miller selected the computers of staff members who were "front and centre" in managing the fallout over the decision to cancel the power plants before the 2011 provincial election.

The trial has heard that Mr. Faist wiped the hard drives in early February, 2013, just days before the transition from the McGuinty government to Premier Kathleen Wynne. In what became known as "Pete's Project," Mr. Faist logged on to the computers using a password assigned to Mr. Livingston's assistant, who had been given special access known as administrative rights.

Mr. Lemon said that Peter Wallace, secretary of cabinet at the time, never would have approved the special access had he known how it would be used. Mr. Lemon described Mr. Livingston as particularly preoccupied with how e-mails are deleted. A memo Mr. Livingston wrote in August, 2012, and presented in court, instructed staff to "double delete" e-mails, to ensure that nothing was turned over to a legislative committee probing the scrapping of the two power plants.

Justice Lipson said the alleged criminal activity is focused on whether Mr. Livingston used "dishonest means" to obtain the administrative rights, and asked Mr. Lemon whether Ms. Miller knew about the "alleged deception" involving Mr. Wallace.

"She doesn't need to know the exact mechanics behind obtaining the password," Mr. Lemon responded. "She knows it has to be obtained with deception."

Scott Hutchison, a lawyer for Ms. Miller, said in his closing arguments that asking Mr. Faist to clean personal information off the hard drives was not a "nuclear option," but a "perfectly normal thing to do."

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If there was some "nefarious plan under cover of night" to wipe the hard drives, Mr. Hutchison said, why did Mr. Livingston seek the administrative rights from Mr. Wallace. "You have people who ask for permission and they get permission," he said.