A jury could possibly find that Dalton McGuinty's chief of staff obtained special access to computer hard drives in the premier's office under "false pretenses" and used it to "destroy data," an Ontario court judge has said in rejecting a defence request to end a criminal trial.

Defence lawyers had sought a directed verdict of acquittal on criminal charges against David Livingston, the chief of staff, and Laura Miller, the deputy chief of staff, arguing there is no evidence they destroyed any government records.

Justice Timothy Lipson is hearing the case without a jury, but said in his ruling that the test on the motion is if there is a complete absence of evidence upon which a jury could conclude an accused person is guilty. But he said some evidence is available upon which a jury could conclude the two were guilty beyond a reasonable doubt.

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Mr. Livingston did not say when he sought the special access known as administrative rights that he intended to indiscriminately delete everything on the hard drives or that he was enlisting someone outside government to do the work, Justice Lipson said in a ruling released on Thursday.

"A jury would be entitled to reasonably conclude that Mr. Livingston dishonestly obtained administrative rights … under false pretenses," the ruling says.

The directed-verdict application calls on the judge to dismiss the charges before the defence has even called any witnesses, arguing the Crown has not proved its case.

While the lawyers did not persuade Justice Lipson of Ontario Court of Justice to toss out the case altogether, the judge did reduce a charge of mischief to attempted mischief. Last Friday, the Crown dropped one of the three charges against their clients.

Mr. Livingston and Ms. Miller were initially accused of destroying e-mails and other government records related to the controversial cancellation of two gas-fired power plants. Prosecution lawyer Tom Lemon asked Justice Lipson last Friday to drop breach of trust charges against the two, saying the Crown cannot prove specific e-mails were deleted.

Defence lawyers sought a directed-verdict of acquittal on the two remaining charges: mischief and unauthorized use of a computer in connection with the wiping of 20 hard drives in the premier's office. Each has pleaded not guilty.

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

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In urging the judge not to dismiss the charges, Mr. Lemon argued that Mr. Livingston and Ms. Miller did not have the authority to erase everything on the hard drives of government computers.

The trial in a courtroom in Toronto's Old City Hall has heard that Mr. Livingston was told in writing to preserve government records, including any documents related to the governing Liberals' decision to pull the plug on the two power plants before the 2011 provincial election. Ontario's Auditor-General has pegged the cost at more than $1-billion.

Justice Lipson says in his ruling that the hard drives were wiped during a period of "considerable tension" at Queen's Park. The decision to cancel the power plants dominated political discussions at the legislature in the months leading up to the transition from the McGuinty government to Premier Kathleen Wynne in February, 2013. Peter Wallace, cabinet secretary at the time, testified that the issue of retaining gas-plant related documents was a "central focus of discussion." The government was under pressure to disclose documents related to the gas plants to a legislative committee probing the matter and in response to freedom-of-information requests.

Mr. Livingston and Ms. Miller either sent or received numerous e-mails regarding issues related to the gas plants that were obtained by police through search warrants and presented as exhibits at the trial, the ruling says.

"A jury would be entitled to conclude that some of the emails ... were documents of long-term business value which should have been retained for the purpose of responding to FOI requests and/or committee production orders," the ruling says.

It was in that atmosphere, the ruling says, that Mr. Livingston and Ms. Miller enlisted Mr. Faist to "destroy data" on the hard drives. Mr. Faist testified that the wiping was "indiscriminate and without regard to content," the trial has heard.

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Justice Lipson says in his ruling that it is not known what records were on the hard drives when they were wiped, or whether they included any that the two accused had a legal obligation to preserve.

"The Crown did not lead forensic expert evidence on what, if any, data was destroyed by wiping the hard drives," the ruling says.

During nearly three weeks of testimony, there was no evidence about whether the hundreds of e-mails that police recovered were from the hard drives in the premier's office or government servers. A retired police officer hired by the Ontario Provincial Police to conduct a forensic analysis of computer hard drives seized from the premier's office was barred from serving as an expert witness for the Crown because he was too close to the investigation.

Justice Lipson said in his decision he is reducing the mischief charge against the two accused to attempted mischief because there was no effort to conceal Mr. Faist's activities – he wiped the hard drives during business hours – and wiped only the hard drives of staffers who were leaving the premier's office.

Scott Hutchison, Ms. Miller's lawyer, told reporters outside the court on Thursday that prosecutors "walked away" from the breach of trust charges when they were faced with the directed-verdict application. And now, he said, the judge has reduced one other charge.

"So far, everything in this case is moving in the right direction," Mr. Hutchison said.

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Mr. McGuinty is not under investigation and has co-operated with the probe.

The trial continues on Nov. 16.