Thibault, who held the provincial vice-regal post between 1997 and 2007, is charged with fraud and breach of trust in relation with more than $700,000 in alleged improper expenses.
Investigator Robert Anctil said Thibault stayed at the Chateau Frontenac Hotel in Quebec City when she was first named to the post.
But as of 2000, she lived exclusively outside the provincial capital, Anctil said. That made her eligible for expenses billed to the federal government.
When federal officials told her the boundaries of Quebec City had changed after municipal merges, Thibault deliberately chose to dine at restaurants that fell outside the area, Anctil testified.
In March 2003, Thibault's chief of security, Guy Hamelin, bought a residence in Beaupre — outside the provincial capital — where Thibault began to live. That entitled her to a $500 monthly federal allowance.
At the same time, Thibault also had a monthly housing allowance of $4,000 from the Quebec government. Plus, she received an additional $800 in fixed costs every month.
"She fled the area to reside elsewhere," Anctil said.
The charges came after a joint report filed by former provincial auditor general Renaud Lachance and his federal counterpart at the time, Sheila Fraser.
They concluded Thibault received $700,000 in expense reimbursements that had nothing to do with her role.
Her duties as lieutenant-governor were similar to those performed at the federal level by the Governor General.
The evidence against Thibault is exhaustive and includes more than 14,000 files.
Anctil said certain expense claims caught the attention of investigators.
One notable claim involved an outing in the Outaouais region in western Quebec. It included rented fishing rods and earth worms that were bought at a hunting shop.
Birthdays, funerals and other family activities were also found to be private activities, the investigator said.
Thibault's lawyer, Marc Labelle, said the definition of official functions of the lieutenant-governor did not exist.
Earlier on Wednesday, Anctil explained that official business necessitated an invitation sent to the offices of the lieutenant-governor. An aide was then assigned to the event and an activity was planned.
The trial finally began after several delays.
Thibault's lawyers tried repeatedly to have the case tossed out by arguing that, as the highest representative of the Crown in Quebec, she could not be prosecuted by herself.
The Supreme Court of Canada refused to hear her case last May.