The prosecution began laying out the allegations against two of former Ontario premier Dalton McGuinty's most senior officials on Friday, marking the second corruption trial involving provincial Liberals this month.

David Livingston, McGuinty's chief of staff in 2012 and 2013, and his deputy chief of staff Laura Miller, are charged with breach of trust, mischief, and misuse of a computer to commit mischief.

They're accused of destroying government documents in two ways: by deleting emails they had sent and received related to the $1 billion cancellation of two gas-fired power plants, and by ordering 21 hard drives in the premier's office be wiped clean.

Laura Miller, deputy chief of staff to former Ontario premier Dalton McGuinty, arrives at court on Friday, Sept. 22. Both Miller and her superior, David Livingston, have pleaded not guilty. (Katherine Brulotte/CBC)

Both Livingston and Miller have pleaded not guilty.

"The allegation is that they destroyed records that they had a legal duty to protect," said Crown lawyer Sarah Egan in her opening statement.

Egan said Livingston and Miller "acted contrary to the public interest" by getting rid of public documents.

The trial is about "the intentional destruction of data for the purpose of thwarting the public' right to accountability and transparency," Egan said.

The allegation is that they destroyed records that they had a legal duty to protect. - Sarah Egan, Crown lawyer

She said evidence will show that Livingston and Miller claimed to have no relevant documents in response to an Access to Information request about the gas plant cancellations, despite their time working in the premier's office at the height of the ensuing controversy.

The court also heard about a January 2013 email Livingston received from the province's Corporate Chief Information Officer, Dave Nicholl, warning him to "preserve any records related to [the gas plants] to avoid any allegation that they were improperly deleted."

It's alleged the hard-drive erasing began one week after that email.

The first witness called was Robert Gagnon, a retired detective-sergeant who previously led the OPP's electronic crime section.

The Crown said Gagnon is expected to testify that a "significant number of emails" were deleted from Livingston's and Miller's computers.

Documents wheeled into court with a dolly

The amount of documents being presented in the case had to be wheeled in by court staff using a dolly — approximately 10 banker's boxes full of paper were brought into the courtroom on Friday.

"I have a feeling this case is going to involve a lot of exhibits," said Ontario Court Judge Timothy Lipson.

The trial is to resume Monday.

Breach of trust is the most serious charge in the case. It's about alleged misuse of public office for personal benefit.

I have a feeling this case is going to involve a lot of exhibits. - Timothy Lipson, Ontario Court Judge

The Supreme Court of Canada set the test for a breach of trust conviction in the case of a Quebec police chief accused of misusing his authority to get his daughter cleared of fault in a car accident.

The Supreme Court ruled unanimously that the Crown must prove an accused showed intent to use their public office for a corrupt purpose.

Livingston's lawyer is Brian Gover, while Miller's defence is led by Scott Hutchison.

Second corruption trial this month

In the other corruption trial that began this month involving Ontario Liberals, Premier Kathleen Wynne's former deputy chief of staff, Pat Sorbara, and Liberal fundraiser Gerry Lougheed Jr. are charged with bribery under Ontario's Elections Act. They're accused of offering a job to a would-be Liberal candidate in exchange for stepping aside in the 2014 byelection in Sudbury.

Sorbara is also facing a second count of bribery, for allegedly offering inducements to Glenn Thibeault, now the province's energy minister, to run in that byelection.

The Crown has finished calling evidence in the Sudbury case. That trial is to resume Oct. 10, when the defence argues for the case to be dismissed.