Following days of zeroing in on Senate rules and definitions of primary residence and partisan activities, the first week of the Mike Duffy trial ended with the Crown making a case against the suspended senator's residency in P.E.I. by using the hypothetical Senate appointment of Justin Bieber.

Mark Audcent, a former Senate law clerk, wrapped up three days of testimony Friday at Duffy's provincial court trial on fraud, breach of trust and bribery charges.

During the week, under questioning by defence lawyer Donald Bayne, Audcent conceded that the Senate administrative rules provide no specific guidelines or definitions on such terms as primary or secondary residence or what constitutes partisan activities.

Skip Scribble On Friday, Bayne continued to advance his argument about the vagueness of the Senate rules, getting Audcent to also concede that senators have "broad administrative discretion" when it comes to deciding how to use their office budgets, including whom they can hire and the duties of their researchers.

The definition of primary residence, partisan activities, the use of a senator's office budget and who they hire are all significant issues at the trial.

On the issue of primary residence, Duffy designated his home in P.E.I. as his primary residence, and maintains that's the case, making him eligible to claim meals and living expenses for his time in Ottawa, even though he has lived in Canada's capital since the 1970s. The Crown disputes that P.E.I. is Duffy's primary residence.

The issue of partisan activities is of significance to Duffy's case as the Crown has accused him of filing Senate expense claims for travel for personal and partisan reasons, unrelated to Senate business.

As well, the use of a senator's office budget and hiring is of importance to the trial, because Duffy is accused of paying his friend Gerald Donohue $65,000 as an independent contractor for "little or no apparent work." Donohue, a former technician who worked for CTV and CBC, told investigators he did internet research and provided verbal advice to Duffy, the RCMP has said.﻿

On this issue, Audcent agreed in court on Friday that senators also have broad discretion as to who can be members of their staff.

"In layman's terms, you hire who you want to do the work you want done," Bayne said.

"Yes," Audcent replied.

Also, Bayne argued, the job description of researchers is "enormously broad." Audcent agreed.

Although Audcent was called as the first witness by Crown prosecutor Mark Holmes, who examined him for less than an hour on Wednesday, it was Bayne who has spent most of the time with Audcent. Bayne has been using Audcent to try to bolster the defence argument that Duffy should not be punished for the Senate's vague rules.

The photo signed by Prime Minister Stephen Harper and dated June 11, 2009, carries the message: 'To Duff. A great journalist and a great senator. Thanks for being one of my best, hardest working appointments ever.' (CBC)

But ﻿Friday afternoon, Holmes was able to question Audcent about some of his testimony. Earlier this week, on the issue of residency, Audcent had said that, according to the Constitution, a potential or current senator must be a resident of the province for which he or she is appointed.

Bayne had argued that since the Constitution required a senator to be a resident of the province they represent, that made their residence in P.E.I. his most important residence, or in other words, their primary residence.

But on Friday, Holmes suggested that becoming a senator doesn't suddenly make you a resident of that province, you need to have already been a resident. To further his point, he raised the Senate requirement that a senatorial candidate must be at least 30 years old to be a senator. And this is when he brought up Bieber.

Bieber, Holmes said, is 21 years old. If the Governor General was to appoint the Canadian singer to the Senate tomorrow, would he become 30, Holmes asked Audcent.

"Of course not," Audcent replied.

The trial resumes on Monday.