Audcent, who helped draft the first real set of Senate administrative rules a decade ago, figures he helped to break in around 100 new senators, briefing them during orientation sessions about the important bits in the Constitution.
The Crown was particularly interested to hear Audcent discuss what the Constitution says about a senator's residency.
Duffy is on trial on 31 charges, which include allegations that he fraudulently claimed living expenses for a home in an Ottawa suburb, where he spent most of his time, while declaring a summer house in P.E.I. as his primary residence.
Duffy had been appointed by Prime Minister Stephen Harper in December 2008 to represent the island, despite the fact he had lived and worked in the national capital for decades.
The Constitution requires a senator to own property worth at least $4,000 in the province that they represent, and that they be resident in the province, Audcent explained.
Initially, his testimony seemed to support the view expressed Tuesday in the opening statement by Crown attorney Mark Holmes, that there is a "common sense" understanding of the meaning of residence.
Determining residency depends on certain indicators, Audcent said, such as where a person lives, pay their taxes, obtain services such as health care and spend social time with activities like bowling or going to church.
"Every indicator is just part of a package; residence is a question of fact," he said, noting that it wasn't his job in the Senate to police residency.
"You gather these indicators together and you look at the whole picture. There is no indicator that is absolute."
During his cross-examination, defence lawyer Donald Bayne went painstakingly through the Constitution, the administrative rules Audcent had helped write, and other Senate policies that mention residency.
He asked Audcent repeatedly to confirm that there were no specific criteria in any of the statutes or rules that defined the meaning of "primary" or "secondary" residence.
"There's no requirement of a minimum number of days or nights spent in your provincial residence?" Bayne asked.
"No," Audcent replied.
"There is no percentage of the year required in your provincial residence?"
"That is correct."
"There is no majority of the year required for provincial residence?"
Bayne went on to review the residency declaration that senators are required to fill out if they want to claim living expenses.
The form itself draws a link between the province the senator represents and their primary residence, with a space to fill out that says, "The address of the primary residence in the province or territory I represent is...."
Bayne referred to Duffy, a former Parliament Hill journalist, as a "rookie senator," and took the court through a political letter that Duffy and fellow Conservative Pamela Wallin — living in Toronto, but appointed to represent Saskatchewan — had received shortly after their appointments.
In it, Christopher McCreery, a former adviser in the office of government Senate leader Marjory LeBreton, insisted the pair had nothing to worry about regarding their residency status.
"I checked all of the authorities on the Senate and residency is not defined," McCreery wrote in early 2009.
"My interpretation of this is that there has been a long-standing convention that so long as a senator owns property in his or her province of appointment that they are allowed to sit as a senator from that province even if they live in Ottawa 99 per cent of the time."
The defence took so much time cross-examining Audcent that his testimony is expected to spill over into Thursday.
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