Sen. Mike Duffy said Thursday he’ll be “happy to co-operate” with anyone investigating the expense scandal that forced him to leave the Conservative caucus, but he won’t quit the Senate.

Speaking to reporters for the first time since he left the Tory caucus last week, Duffy said “Canadians deserve answers” and called for an “open inquiry” into the spending controversy.

“I think Canadians have the right to know the facts and I’m quite prepared…to give them the whole story,” he said as he left Parliament Hill.

“Hold your horses, it will all come out in due course,” Duffy added when reporters pressed him for details.

Before he got into his vehicle and drove off, Duffy dismissed the notion of resigning from the Senate.

Asked if he would stay in the Red Chamber, Duffy said: “Pffft…of course. I’m a senator. Why wouldn’t I?”

Senate Speaker Noel Kinsella confirmed Thursday that the RCMP’s sensitive and international investigations unit is looking at the expense claims of Senators Duffy, Mac Harb and Patrick Brazeau. The Mounties have asked for Senate’s documents related to claim policies, he said.

In a letter to the Senate, the RCMP said those documents are needed “to make a determination on whether there are grounds to commence a criminal investigation.”

All three senators had invalid expense claims that required taxpayers to be reimbursed, but Duffy paid back just over $90,000 before an external audit was released.

CTV News has also learned that the Mounties contacted the auditing firm Deloitte.

Fife revealed last week that Prime Minister Stephen Harper’s chief of staff, Nigel Wright, wrote Duffy a $90,000 personal cheque to cover his debt to the Senate.

Fife also revealed that the final version of Duffy’s audit report was whitewashed to remove some damning language that accused him of breaking the Senate’s residency rules.

Harper has denied any knowledge of the secret deal between Duffy and Wright.

In Colombia on a trade mission, Harper said Thursday that he was not aware of “any formal agreement” between the two.

Harper also stressed that Wright no longer works for him and will have to answer to the ethics commissioner about his actions.

“We’ve always said when these kinds of things occur we’ll take action and deal with them and hold people accountable. That’s what we’ve done and I think Canadians will understand that,” Harper said while acknowledging that “perhaps” he should have accepted Wright’s resignation earlier than Sunday.

Asked Thursday if he thought the prime minister knew about the cheque, Duffy said: “I have no idea.”

The news of RCMP’s involvement prompted questions from the opposition in the House of Commons Thursday, with NDP MPs asking how the federal government plans to aid the investigation.

“Now (the Conservatives) say they want to help us get to the bottom of this, so who exactly has the prime minister called in to investigate?” NDP MP Charlie Angus asked. “Who has he spoken to and what phone records, memos, emails or cheque stubs have been handed over to help the investigation? Now that the RCMP are involved, what have they done to help?”

Heritage Minister James Moore, speaking for the government in question period, would only say that both the Ethics Commissioner and the Senate ethics office are looking into the Senate expense affair, which has also been referred back to the Senate’s internal economy committee.

On Wednesday, CTV News learned that the order to sanitize an audit of Duffy’s expenses came from two key Conservatives on that Senate committee: Chair David Tkachuk and Carolyn Stewart Olsen.

The original version of the audit said Duffy broke the rules when he declared his cottage as his primary residence and noted that the senator refused to co-operate with independent auditors.

In a phone interview with CTV News Thursday, Tkachuk denied that Duffy’s audit was whitewashed. He also denied that Wright told him to change the wording in the report.

“When we’re writing a report, I talk to all kinds of people,” he said. “Nigel didn’t tell me anything. He didn’t tell me what to do.

“I never talked to him specifically about the report once.”

However, Tkachuk did say that he spoke to Wright about the expense scandal “on a couple of occasions” and that the prime minister’s former right-hand man “expressed his concern.”

“We discussed political matters. This was hurting us,” Tkachuk said, adding that there was “nothing untoward” about his conversations with Wright.

Government Senate Leader Marjory LeBreton told CTV’s Power Play that the language in Duffy’s audit was different from that in the reports detailing Harb’s and Brazeau’s expenses because Duffy had already repaid the money owed.

“I certainly didn’t interfere with the process,” she said, adding that she’s

quite certain” that the PMO didn’t, either.

In question period Thursday, Angus asked about who asked that the language be changed.

“On Feb. 17, the prime minister told this house that Mike Duffy met the residency requirement for the Senate, but he didn’t tell the people of Canada that the Senate had found that Duffy was ineligible to claim his status in Prince Edward Island. But this key passage was removed from the Senate audit by Senator Tkachuk and Senator Olsen,” Angus said.

“Now Carolyn Stewart Olsen has been this prime minister’s closest adviser for 10 years, she is as close as you can get. So who in the Prime Minister’s Office made the call to Olsen? Now that the RCMP are involved, who helped Wright and who helped Olsen in this cover-up?”

“Simply not the case,” Moore replied.

Senators speak out

Earlier Thursday, two Conservative-appointed senators said the rules governing the Red Chamber are simple and it's difficult to understand how some from within their ranks could misinterpret the definition of "primary residence."

Senators Larry Smith and Nancy Greene Raine spoke amid the deepening scandal surrounding housing expenses improperly filed by Duffy, Brazeau and Harb.

"I was very disappointed and surprised and I really don't find the rules complicated,” Greene Raine told CTV's Canada AM from Ottawa.

“I find it very straightforward and if you were ever having any questions, there are all kinds of resources you could go to for clarification."

Quebec Sen. Larry Smith echoed Greene Raine's comments.

"The rules are pretty simple to understand and I have a very difficult time understanding how someone would fail to understand what a primary residence is," Smith said.

At issue of the ongoing Senate scandal is the fact that Duffy, Brazeau and Harb were found to have improperly claimed a housing allowance available to senators whose primary residence is located more than 100 kilometres outside of Ottawa.

The allowance is meant to compensate those required to maintain a secondary residence in the national capital region while working in the Senate. But recent external audits by Deloitte found that all senators spent significantly more time in Ottawa than in their hometowns.

Liberals call for transparency

Meanwhile, Liberals held a news conference Thursday calling for transparency on the issue and asking Canadians to sign an online petition to express their views on the subject.

Liberal MP Ralph Goodale said the Conservatives have misled Canadians about the paper trail related to the scandal. He said the government has maintained there are no documents proving the $90,000 payment was part of a deal with Duffy, but pointed out they have not denied there is at least one email containing details of the transaction.

"Where is that Feb. 20 email that outlines the parameters of a deal?" Goodale asked, citing an email in which Duffy said Wright worked out a "scenario" where all of his claimed living expenses would be covered, including "cash for the repayment." That email was first revealed by Fife.

"Throwing the bodies under the bus is not accountability and crocodile tears from Peru will not do. All the threads here lead to the prime minister. He appointed these people, they were accountable to him," Goodale said.

With files from Andy Johnston