Here are some highlights from the first day:
Duffy enters a plea
It's been a while since the senator has been seen in public and on his walk into the Ottawa courthouse, he was surrounded by cameras and reporters eager for a few words. But the former broadcaster was mum until after all 31 charges were read in open court.
"I'm not guilty, Your Honour," Duffy said in a strong clear voice, as he stood alongside his defence lawyer Donald Bayne.
Joining Duffy in the courtroom was his wife Heather, who may also be called as a witness in the trial. Duffy was mute as he left the courthouse for the day.
Though hundreds of pages of letters, affidavits, emails and other records were already made public in the lead-up to the trial, the actual start of proceedings prompted hundreds more to be tabled into evidence by the Crown.
They've entered seven different books of exhibits, each pertaining to different elements of the charges.
The records include expense forms Duffy filed to the Senate for trips the Crown alleges were personal business, to copies of contracts Duffy had with a friend of his, which the Crown alleges were essentially fronts for Duffy to funnel money.
Is Duffy eligible to be a senator?
The basic issue at trial is whether Duffy committed criminal acts in the way he handled his expenses while a senator and in the subsequent repayment of those expenses by way of a cheque given to him by the prime minister's former chief of staff.
But the Crown raised another question: whether Duffy ought to be a senator at all. He was appointed to represent Prince Edward Island, but the Crown suggested that by virtue of where he was mainly living — a suburb of Ottawa — it may not have been constitutional for the prime minister to appoint him to represent the island.
The defence threw cold water on the proposition, noting that both the prime minister and his office have said many times that Duffy was indeed eligible to be the senator for P.E.I.
The witness list
Dozens of people have been subpoenaed to appear as witnesses at the trial, including journalists, senators, clerks and former staff in the Prime Minister's Office. But the prime minister himself is not among them.
During an event Tuesday in Vancouver, Harper said he's not been called to testify. He has long insisted he didn't know that his former chief of staff Nigel Wright had paid $90,000 to cover Duffy's disallowed expenses.
Harper said investigators have looked into his assertions and have confirmed his position.
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