The crown alleges Duffy set up a slush fund of almost $65,000 with Gerald Donohue to pay for services the Senate would not cover, such as makeup and personal training.
Eight of the 31 charges Duffy faces relate to the Senate contracts awarded to Donohue.
Sen. Mike Duffy arrives at the courthouse for his trial. (Photo: Fred Chartrand/CP)
Duffy has pleaded not guilty to all of the allegations.
The RCMP allege Donohue received the contracts for "little or no apparent work."
The defence has tried to argue that Donohue had legitimate contracts as a consultant and he completed Senate-related work for Duffy.
Duffy and Donohue's relationship dates back to when they both worked in broadcasting.
Court proceedings are set to resume again on Tuesday, when Sen. George Furey is expected to testify.
Duffy's lawyers have yet to confirm when the senator will take to the witness box.
Attention paid to the trial has sharply declined since the Conservatives were defeated in last month's election.
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