Stephen Harper says there's no need to hear an explanation from a Deloitte auditor who allegedly intervened in an independent audit into Mike Duffy's expenses at the behest of the Conservatives' top fundraiser and the Prime Minister's Office.

Mr. Harper said in Question Period Thursday that a trio of Deloitte officials, who testified to a committee last week, was enough to explain the firm's role in the Duffy saga. In doing so, he rejected a call to invite Deloitte's Michael Runia, who has not testified and who RCMP allege called the Duffy auditors at the urging of Conservative senator Irving Gerstein. RCMP say Mr. Gerstein, the Conservatives' fundraising chief, was in talks with Mr. Harper's office over how to approach the situation.

"Why are they blocking Runia if they've got nothing to hide?" New Democrat Leader Thomas Mulcair asked in Question Period Thursday.

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"As you know, the auditors already have in fact testified before the Senate, and have testified as to the integrity of their audit," Mr. Harper replied.

The response came a day after Conservative senators voted down a motion to call in Mr. Runia to explain himself. On the same day, Mr. Gerstein unilaterally rejected a Senate committee motion that he step down as chair unless he explained his own role.

The Senate has now twice rejected a move to call in Mr. Runia. Without it, it doesn't appear he'll speak any time soon. Asked if Mr. Runia would do an interview, a Deloitte spokesman said Thursday that RCMP investigations into the Duffy ordeal are ongoing, and "it would be inappropriate for us to provide further comment while these investigations continue."

On Thursday, Mr. Harper also gave his second defence of Mr. Gerstein in as many days. Mr. Gerstein – his party's chief fundraiser, appointed to the Senate by Mr. Harper – has also repeatedly declined to comment on his role.

"The senator is not under investigation. There are no allegations against him," the Prime Minister said Thursday when asked about his fundraiser, a self-described party "bagman."

RCMP documents suggest Mr. Gerstein and Mr. Runia are key figures in the weeks that preceded the repayment of Mr. Duffy's expenses, which was done in secret at first.

The ordeal dates back to early this year, when the Prime Minister's then chief of staff, Nigel Wright, was trying to facilitate repayment of expenses claimed by Mr. Duffy, who Mr. Harper appointed to the Senate. RCMP allege that, at one point, those expenses were thought to be $32,000, and RCMP say Mr. Wright told investigators that Mr. Gerstein had agreed to pay that sum with the Conservative Party's fund, which Mr. Gerstein chairs. Mr. Gerstein told RCMP he was only considering paying the expenses with the fund, according to a police document.

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The figure was later found to be $90,000, and the plan fell apart. Instead, Mr. Wright wrote a personal cheque to cover the expenses, a fact that was never revealed publicly until a media report. Mr. Harper has said that's when he found out, while RCMP allege Mr. Gerstein was among those who knew about the payment. RCMP are now investigating the payment. Mr. Wright has resigned from Harper's office and Mr. Duffy has been suspended from the Senate.

The RCMP's allegations have not been proved in court.

Mr. Gerstein is also alleged to have called his contact at Deloitte, Mr. Runia, about the Duffy audit. The two men know each other from Deloitte's work auditing the Conservative Party's own books, RCMP allege. RCMP also say Mr. Gerstein made that call after speaking with an official in Mr. Harper's office. There are varying accounts of what information Mr. Gerstein was seeking about the audit.

Last week, a trio of Deloitte officials – none of them Mr. Runia – appeared before a Senate committee and confirmed Mr. Runia did indeed call one of the people carrying out the review of Mr. Duffy's expenses. Deloitte insists no information about the confidential, independent audit was released, but declined to speculate on why one of its employees, Mr. Runia, would seek that information in the first place.

"At no time was any communication regarding the status of the forensic examination or the findings shared with anyone other than the Senate subcommittees and the Senate staff involved in the process. The utmost confidentiality of all forensic examination information was maintained at all times," Deloitte spokesman Vital Adam said in a statement Thursday, in which he said Mr. Runia won't be commenting publicly.