When, as expected, Mike Duffy takes the witness box in Ottawa courtroom 33 this week, the senator will tackle what he has been itching to do since his trial began — offer, in his own voice, his defence against the 31 charges of fraud, bribery and breach of trust he now faces.

It's a legal strategy that comes with both advantages and pitfalls, but at the same time it would almost certainly be the most compelling chapter of the defence narrative put forth by Duffy's lawyer Donald Bayne since the trial began in early April.

"The whole point of cross-examination is to build the defence case in a coherent way, you are telling a story. And usually that crescendos with your client completing the story," says Jason Neuberger, a Toronto-based criminal lawyer who has been following the trial.

One of Bayne's goals, Neuberger says, is to re-establish the senator's credibility. "It's' very hard now to complete that picture without him testifying."

The Duffy trial resumes Monday at 9 a.m. ET, when the Crown is expected to call its final witness, Senator George Furey. Furey was appointed Speaker of the Senate last week, but in 2013 was the Liberal representative on the committee that changed an audit report on Duffy's expenses.

As for the garrulous Duffy, this week will be his first chance to speak at length publicly since before the trial began. He has stayed largely silent, ignoring the throngs of reporters as he would enter and exit the Ottawa courthouse. However, Bayne has repeatedly said that his client would testify on his own behalf.

If that happens, this will be his opportunity to justify, legally, his series of controversial expense claims — expenses the Crown contends were not related to Senate or government business and should not have been billed to the taxpayer.

He may also see this as his moment to try to rehabilitate his political and public reputation.

How long Duffy would be in the witness box is hard to say. Some of the Crown witnesses spent days facing a barrage of meticulous cross-examination by Bayne.

Bayne is likely to be just as thorough with his client, delving through all the allegations, while allowing Duffy to comment and provide explanations.

Chief among them will be the fact that Duffy, a senator representing P.E.I., had designated his home in that province (a renovated cottage) as his primary residence, which he felt allowed him to claim, under Senate rules, housing expenses for his house in Ottawa.

But the Crown has argued that his primary residence was, in fact, in Ottawa, where he owned a home and had lived most of his adult life, meaning he was ineligible for these claims.

Travel claims

Bayne will likely also take Duffy through the series of travel expenses he claimed for events that the Crown contends had nothing to do with government business. Those included partisan fundraising events, a B.C. luncheon, private funerals, and a Peterborough, Ont., dog show.

Sen. Mike Duffy, who has pleaded not guilty to 31 charges of fraud, breach of trust and bribery, is expected to testify this week at his trial in an Ottawa courtroom. (Fred Chartrand/Canadian Press)

Duffy will also have to explain the business arrangement that he developed with his friend, Gerald Donohue, in which Donohue received $65,000 worth of government contracts.

It was from that pool of money that Donohue wrote cheques for expenses — including for a personal fitness trainer, makeup artist and professional photos — incurred by Duffy, and which the Crown says would not have been approved by Senate finance officials and were therefore ineligible claims.

Then there's that $90,000 payment of Duffy's outstanding expenses by Stephen Harper's former chief of staff, Nigel Wright. Accepting that constituted a bribe, the Crown alleges.

Throughout the trial, Bayne has meticulously attempted to counter all the Crown's charges. He has suggested that his client broke no Senate rules as the rules were vague and ambiguous. and he has argued that Duffy's travels were all related to Senate business, as were any expenses he claimed.

The arrangement with Donohue, while "administratively irregular" was not illegal, Bayne has proffered. And the alleged bribe? Nonsense, he suggested, arguing that the whole arrangement was forced upon his client by the former prime minister's office trying to make a controversy go away.

Double-edged sword

Bayne is a very skilled courtroom lawyer and has certainly thought his strategy through. But Neuberger says that a Crown's case can often be rehabilitated by putting the accused in the witness box.

Having Duffy testify might damage the success that his lawyer has had on cross-examination of other witnesses.

Donald Bayne, Duffy's lawyer, will likely delve through all the allegations against his client, while allowing the senator to comment and provide explanations. (Justin Tang/Canadian Press)

Given the number of allegations of fraudulent conduct that the senator faces, by not testifying and leaving the evidentiary record as it is, he runs the risk of being convicted on some of those charges, suggests Ottawa-based lawyer Jason Gilbert, who has also been following the case.

While Bayne has been quite effective at neutralizing some of the more high-profile fraud allegations, some of the housing, travel and other expenses need to be addressed by Duffy himself, Gilbert feels.

"I think if it's just kind of left out in the open, sort of dangling out there, without being commented on or potentially an explanation from Mike Duffy, he may stand to face conviction of some of that."

Still, Neuberger says "there are certain expenditures and issues I think a crown attorney will enjoy cross-examining him on. So it's a tough call in this case."

The big concern for Duffy, says Neuberger, is that that the Crown will be given a platform to challenge Duffy's decision-making.

He could face questions, Neuberger suggests, like: 'Well Mr. Duffy, you're a very bright man who has covered politics for 30 years of your career as one of the most leading political reporters and analysts in Canada. Surely an expenditure for X, in your mind would not be related to your government business. Right?"

Still, there are also serious advantages for Duffy testifying in his own defence.

"The real benefit is [Duffy] getting out in front of it, and saying 'I thought these were legitimate, here's why, the rules were very all over the place,'" Neuberger says. "He might explain why certain expenditures that look absurd are not. He might simply say 'I always thought that these expenditures were legitimate.'"