The RCMP has begun interviews on Parliament Hill into Senator Pamela Wallin's expenses, CBC News has learned.

Two Mounties are involved, questioning other senators and Senate officials.

Marjory LeBreton, the former government Senate leader, confirmed to CBC Thursday she met with the RCMP within the past two weeks regarding Wallin. LeBreton did not want to talk about what kind of questions she was asked.

In an email, she said, "I think it would be inappropriate to divulge any further information. I believe it is important to fully co-operate with the RCMP and then let them do their work."

Other senators have scheduled meetings with the RCMP for mid-October, just before Parliament returns. The timing means the Senate expense scandal will be top-of-mind in the fall, even though Prime Minister Stephen Harper prorogued Parliament in order to have a fresh start in the second half of his mandate.

Mounties have specific questions about Wallin

Sources close to the investigation say there are specific issues the RCMP is interested in pursuing. The Mounties who conduct the two-hour interviews want to know more about information revealed in the Deloitte audit of Wallin's expenses.

They are asking pointed questions about the changes she made to her calendar. 

Wallin, in a statement after the Deloitte audit was made public, admitted she made changes to her calendar, saying, "I was advised partway through the process that I should only include information relevant to the actual expenses being claimed. So we formatted our calendar accordingly and added as much additional information as we had regarding the claims, without irrelevant, private or personal information included."

The police interviewers are also asking about any advice Conservative Senator David Tkachuk might have given Wallin about changing her calendar. Wallin has said, in a letter to Deloitte, that Tkachuk advised her and her lawyer that the audit on her expenses had been expanded, and she would be better off not providing as much information about her travel claims.

Tkachuk, who in June resigned as head of the Senate committee that monitors senators' expenses, has said he did not ask Wallin to change her calendar, but merely counselled her to avoid providing "irrelevant" material.

Wallin repaid $140K-plus but says no wrongdoing

The police are also interested in Wallin's claim that Harper told her she would have special responsibilities as an activist senator when she was appointed.

As well, they are asking about Wallin's Senate schedule and her corporate schedule.

The Mounties would also like to know why the Senate, after reading and accepting the Deloitte report, made the decision to refer Wallin's expense claims to the RCMP.

The Mounties looking into Wallin's case are different members of the force than those investigating Senator Mike Duffy, who repaid $90,000 to the Senate for inappropriate expense claims using a cheque from Harper's then chief of staff, Nigel Wright, who resigned after the cheque came to light.

In August, the Senate's internal economy committee received the Deloitte independent audit of Wallin's expenses. The audit assessed more than $500,000 worth of Wallin's travel claims and determined that about $100,000 of those were inappropriate or questionable.

In response, the Senate committee imposed restrictions on Wallin's travel and demanded she repay tens of thousands of dollars. And it referred the audit to the RCMP.

The RCMP has not said publicly whether it has opened an investigation.

Earlier this month, Wallin paid back about $140,000 in expense claims plus interest, although she maintains she did nothing wrong.