Criminal charges against two senior staffers in former Ontario premier Dalton McGuinty's office should be dismissed because there is no evidence they destroyed any government records, their lawyers argue.

The Crown agreed on Friday to drop one of three charges against David Livingston, who was Mr. McGuinty's chief of staff, and Laura Miller, the deputy chief of staff. Prosecution lawyer Tom Lemon said in court in Toronto's Old City Hall that the Crown does not have a "reasonable prospect" of getting convictions against Mr. Livingston and Ms. Miller on one count each of breach of trust.

The decision leaves the two facing mischief and unauthorized use of a computer charges in connection with the destruction of e-mails and other government records. They have pleaded not guilty.

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On Friday, their lawyers sought a directed verdict of acquittal on the two remaining charges facing their clients.

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 proven its case.

Brian Gover, a lawyer for Mr. Livingston, told the court the Crown's case "borders on a conspiracy theory." Any suggestion that files deleted in the premier's office contained work-related documents is just speculation, he said.

Scott Hutchison, Ms. Miller's lawyer, said there is no evidence the two accused destroyed any documents that they were required by law to retain.

"The only way the Crown can prevail is if they can show there was a deliberate effort to destroy a document that someone was required to keep," he said.

Much of the Crown's case hinges on circumstantial evidence. 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.

A retired police officer retained 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.

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Justice Timothy Lipson of the Ontario Court of Justice ruled in September that the officer was too close to the police investigation and therefore biased. As a result, it has not been made clear during nearly three weeks of testimony from other witnesses whether e-mails presented as exhibits in court were recovered from the hard drives or other computer servers. Court has also not been told what records existed on the hard drives before they were wiped.

In response to the directed verdict application, Mr. Lemon asked the judge to take into consideration the environment at the provincial legislature when the documents were deleted. The governing Liberals were facing a growing scandal over their controversial decision to cancel two gas-fired power plants before the 2011 provincial election, and were under intense pressure to produce records. The purging of documents took place while the issue of document retention was "front and centre," he said.

Mr. Gover argued that Mr. Livingston's motives for hiring Mr. Faist – who did not have security clearance to work in the premier's office – were much more benign: He wanted to delete personal information from the hard drives before the transition from the McGuinty government to Premier Kathleen Wynne.

Judge Lipson noted that the defence lawyers were asking him to draw the inference that there was nothing of value to erase, and yet Mr. Livingston and Ms. Miller had gone to the trouble of getting special access to the hard drives, known as administrative rights, and of paying Mr. Faist to do the work.

"Why would they go to such extraordinary lengths to get into those computers if they didn't think there was something to get rid of?" the judge asked.

The Crown argues in its written response to the directed verdict application that wiping the hard drives was part of a larger attempt to ensure that there were no recoverable records, which could demonstrate that Mr. Livingston and Ms. Miller did, in fact, have records that were responsive to a freedom-of-information request related to the cancelled power plants. Both had claimed they had no records. The Crown's brief, tabled in court, also says the two accused wanted to ensure that no documents remained for any future orders by a legislative committee to produce records.

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"The wiping was indiscriminate," the Crown says in its brief. "All files on those hard drives were eliminated, without regard to content or record keeping obligations."

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

The trial continues on Tuesday.