Liberal Sen. Joan Fraser moved a motion Tuesday asking that Deloitte managing partner Michael Runia be called to testify before the Senate's internal economy committee.
But Conservative senators argued that such a move might interfere with an RCMP investigation into a deal cooked up by Nigel Wright, the prime minister's former chief of staff, to give Duffy $90,000 so that he could reimburse the Senate for invalid expense claims.
"I accept that there are or may be concerns or potential concerns raised" about interference in the audit, Conservative Sen. Vern White told the Senate.
"But my focus is not on whether or not the committee should hear from Mr. Runia but rather that this should not occur in the midst of the criminal investigation presently being conducted," he added, arguing that Runia is a potential witness.
Liberals questioned the Conservatives' logic, noting that they brushed off concerns about interfering with the RCMP investigation last month when they voted to suspend Duffy and two other senators — Pamela Wallin and Patrick Brazeau — whose expenses are also under police probe.
The vote on Fraser's motion was deferred until Wednesday evening.
The Liberal push to hear from Runia follows the bombshell disclosure two weeks ago of emails exchanged among top PMO aides and key Tory senators that suggest the PMO tried to ensure the Duffy audit would make no finding about whether his primary residence was in Ottawa or Prince Edward Island, the province he was appointed to represent.
The emails, filed in court by the RCMP, show that Wright asked Sen. Irving Gerstein to speak to his "senior contacts" at Deloitte about the audit. Deloitte audits the books of the Conservative party's fundraising arm, which Gerstein heads.
Runia even gave a presentation at the Conservative party's national convention in Calgary in October, according to Liberal Senate leader James Cowan.
Gary Timm, the lead auditor on the Duffy file, last week told the internal economy committee that he received a call from Runia, who wanted to know how much Duffy would owe if his expense claims were ruled invalid. Timm said he reminded Runia it would be inappropriate to discuss the confidential audit and cut the call short.
Timm and two other members of his audit team insisted that their audit was in no way influenced by Runia or anyone else.
Having got that assurance, Claude Carignan, the government leader in the Senate, accused the Liberals on Tuesday of "becoming too partisan by wanting to pursue this endlessly."
But Cowan argued it "strains credulity" to believe the PMO wanted Runia to find out how much Duffy owed when the $90,000 tab was already known at that time.
"Why bring out your big guns, why take steps that you had to know break the critical ethical wall of the audit for information you already have?"
Moreover, Cowan noted other emails show that top PMO aides seemed to have advance knowledge that the Duffy audit would not be able to make any finding about the senator's primary residence because he had refused to meet with the auditors.
Indeed, he said that advance knowledge allowed the PMO to have "a very significant impact on the conduct of the audit" in that it resulted in the PMO instructing Duffy to continue refusing to co-operate with the auditors.
"If we fail to do everything in our power to ascertain what exactly transpired here, then colleagues, we are ourselves complicit in this sordid affair," Cowan told the Senate.
Conservative Sen. Don Plett, who voted against suspending Duffy, Wallin and Brazeau for fear of jeopardizing the RCMP investigation, said he has the same concern about calling Runia and Gerstein to testify before committee.
Asked outside the chamber if his Tory colleagues are being hypocritical in adopting his argument now when they ignored it during debate on the suspensions, Plett said: "I need to worry about me not being hypocritical, not other people."
Cowan pointed out that unlike the three suspended senators, who are actually the focus of RCMP probes, neither Runia nor Gerstein are themselves being investigated so far as anyone knows.
Gerstein, who also allegedly offered have the party pay Duffy's expense tab when he thought it would amount to no more than $32,000, declined to comment Tuesday on his role in the affair.
"There's an investigation taking place by the RCMP, and I'm co-operating fully," was all he would say.
Meanwhile, the federal information commissioner has launched an investigation into the mysterious disappearance and reappearance of emails related to the Senate expenses scandal.
Suzanne Legault's office confirmed Tuesday an investigation has been initiated in response to a complaint from deputy Liberal leader Ralph Goodale.
Goodale had submitted an access-to-information request to the Privy Council Office, seeking all emails, correspondence and other records related to the Wright-Duffy deal.
The PCO, which provides bureaucratic support to the PMO, eventually responded in late June that, after a thorough search, no records were found.
Since then, however, documents obtained by the RCMP from the PMO and filed in court, have disclosed hundreds of emails exchanged between Wright, Duffy, Perrin, various other top aides in the PMO and several senators.
Moreover, PCO acknowledged Sunday that it mistakenly told the RCMP that Perrin's emails had been deleted when he left the government's employ in March, according to standard practice. In fact, Perrin's emails had been preserved because of his involvement in an unrelated legal matter.
The email trail disclosed by the RCMP so far shows Perrin was intimately involved in negotiating a deal with Duffy's lawyer, under which Duffy agreed to repay his expenses on condition that he be fully reimbursed, that an audit into his expenses be halted and a Senate report on his expense claims be whitewashed.
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