The RCMP are investigating Senator Pamela Wallin for allegations of fraud and breach of trust related to her expense claims, new court documents say.

The documents, filed in an Ottawa court this week, allege that Ms. Wallin used "deceit, falsehood, or other fraudulent means" to defraud the Senate of more than $5,000. They also reveal that Senate staff cautioned Ms. Wallin about her expenses on several occasions beginning in September, 2009 – well before a formal audit of her claims was launched.

Ms. Wallin is one of three senators facing possible suspension from the Senate without pay. An external audit conducted this year found that she had charged the Senate for dozens of personal and business expenses she was not entitled to claim.

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The Saskatchewan senator has said in the past that she may have made mistakes in filing some of her expenses, but has also insisted she did not intentionally charge the Senate for unrelated expenses. However, the documents filed by the RCMP suggest that Ms. Wallin was warned about her claims on several occasions over the past four years.

The Senate's director of finance, Nicole Proulx, told RCMP investigators that she and the Clerk of the Senate, Gary O'Brien, cautioned Ms. Wallin about her claims in 2009, noting that any business she conducted in Toronto – where Ms. Wallin owns a condo – "had to comply with Senate policy," according to the documents.

In January, 2012, they again raised concerns with Ms. Wallin about "irregularities" with her claims, Ms. Proulx told the RCMP. The concerns related to a high percentage of travel claims that had been filed without a specific purpose listed, a high percentage of stopovers that were claimed in Toronto for Senate business, and the cost of Ms. Wallin's car services, the court documents say.

Ms. Proulx told RCMP investigators that, on several occasions in 2010, claims for some of Ms. Wallin's car services were rejected by Senate finance officials. However, those decisions were later reversed after Ms. Wallin brought the matter to a special Senate committee for review, according to the RCMP records.

In late 2011, the Senate's finance audit co-ordinator was asked to look at claims related to Ms. Wallin's stopovers in Toronto for a time period covering April, 2011, to the end of December, 2011.

A spreadsheet of the claims was presented to Senate administrators and to Conservative Senator David Tkachuk, then the chair of the Senate's internal economy committee. After receiving a letter from a former assistant to Ms. Wallin in August, 2012, Mr. O'Brien asked for a more comprehensive review of the senator's claims.

Ms. Wallin has argued that the audit of her expenses, perfomed by Deloitte, applied newly adopted travel policies to her claims retroactively, a suggestion that is disputed by the RCMP in the court documents.

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Her lawyer, Terrence O'Sullivan, said Friday that he was not able to comment on the suggestion that Ms. Wallin had been warned about her expense claims in the past. "We believe that an objective review of all the evidence will demonstrate that there was no attempt to defraud the people of Canada," Mr. O'Sullivan said.

The documents were filed by the RCMP's national division on Oct. 28 to support demands for evidence from the Senate and the auditors, including a copy of Ms. Wallin's electronic calendar, records of expense claim payments to Ms. Wallin and recordings and notes from interviews conducted by the Deloitte auditors.

Ms. Wallin was appointed to the Red Chamber by Prime Minister Stephen Harper and began serving as a senator in 2009. She was removed from the Conservative caucus earlier this year amid a growing controversy about her expense claims.

Senators Mike Duffy and Patrick Brazeau, and former senator Mac Harb, are also under investigation by the RCMP in connection with their expense claims. None of the senators under investigation have been charged.