OTTAWA - The first criminal charges to emanate from the year-long Senate expenses scandal have been laid against Mac Harb and Patrick Brazeau — and they likely won't be the last.

Harb, a former Liberal senator who resigned from the upper house last summer, and Brazeau, a former Conservative senator who was suspended from the Senate last fall, face one count each of fraud and breach of trust in relation to their travel and living expense claims, the RCMP said Tuesday.

The Mounties continue to investigate allegedly fraudulent expenses claimed by suspended senators Mike Duffy and Pamela Wallin.

They are also investigating Nigel Wright, who was Prime Minister Stephen Harper's chief of staff when he personally gave Duffy $90,000 to reimburse the Senate for disputed living expenses.

"I can assure you that we continue our work on other significant files," assistant commissioner Gilles Michaud, commanding officer of the RCMP's national division, told a packed news conference.

"RCMP investigators continue to explore multiple leads, to ascertain all the facts and collect the evidence in support of these facts."

Given the explosive political nature of the investigations, Michaud took pains to emphasize that they are being conducted in an "exhaustive and unbiased" manner with "diligence and professionalism."

During the course of its investigation of Harb, the RCMP at one point alleged in court documents that the former senator had engaged in mortgage fraud. However, Michaud said the force ultimately concluded the evidence did not support those allegations.

Tuesday's charges stem from allegations that Harb declared two largely unused country homes as his primary residences, allowing him to claim a Senate housing allowance and living expenses for his supposed secondary residence in Ottawa — where he had lived for years prior to his 2003 appointment to the Senate and where he continued to spend most of his time.

Although he has always denied any wrongdoing, Harb repaid the Senate $231,649.07.

Harb's lawyer, Sean May, said the former senator and one-time MP will defend himself "vigorously."

"He'll be pleading not guilty and maintaining his innocence and taking the matter to trial," May said in an interview, predicting that the trial is "a year or more away."

The Mounties allege that Brazeau fraudulently claimed his father's home in Maniwaki, Que., as his primary residence, although he was rarely seen there and lived primarily just across the river from Ottawa in Gatineau, Que.

Brazeau had no immediate comment. But, like Harb, he has maintained that he did nothing wrong and was tripped up by ambiguous Senate rules.

An independent audit of the pair's expense claims last spring said Senate rules on primary residences lacked clarity and, therefore, the auditors could not determine whether either senator had broken the rules.

Notwithstanding that conclusion, the Senate's internal economy committee declared the rules to be "unambiguous" and demanded that the senators repay their disputed expense claims.

Harb complied but Brazeau refused to reimburse the $48,000 he was asked to pay back, prompting the Senate to garnishee his salary.

However, he was subsequently suspended without pay from the Senate last fall, along with Duffy and Wallin.

In a separate legal imbroglio, Brazeau faces charges of assault and sexual assault, which were laid after an incident at his home last February.

Wallin has reimbursed the Senate for almost $150,000 in dubious travel expense claims.

The fact that Wright gave Duffy the money to reimburse his living expense claims has complicated his case, with the RCMP alleging the two men engaged in fraud, bribery and breach of trust.

RCMP documents filed in court have suggested that Wright orchestrated a scheme in which Duffy agreed to repay his expenses on condition that he be reimbursed, that a Senate report on his conduct be whitewashed and that an independent audit would not question his right to sit as a senator for P.E.I., although he lived primarily in Ottawa.

Wright has insisted his intentions were noble and that he did not break the law.

The court documents suggest more than a dozen others, including staffers in the Prime Minister's Office, at least four Conservative senators and Conservative party officials, were involved in the deal. Harper maintains he knew nothing about it until news of the deal leaked out last May.

In the House of Commons on Tuesday, NDP Leader Tom Mulcair laid blame for the scandal on Harper, who appointed Duffy, Wallin and Brazeau.

"Does the prime minister understand that the Senate scandal began when he started naming senators from places where they didn't even live?" Mulcair asked.

For his part, Harper congratulated the RCMP for finally laying some charges, after almost a full year investigating the scandal.

"We expect all parliamentarians to respect the rules and respect the law and, if they do not, there will be consequences," Harper said. "We obviously salute and acknowledge the work of the RCMP on these particular cases."

NDP ethics critic Charlie Angus called on Harper and Liberal Leader Justin Trudeau to "come clean" on any other senators who've made improper expense claims. And he called on auditor general Michael Ferguson, who is looking at each senator's expenses, to name anyone found to have made improper claims and refer the cases to the RCMP.

Perhaps anticipating more problems among Liberal senators, Trudeau last week ejected all 32 senators from the Liberal caucus, although they continue to sit as Liberals in the upper house.

"I trust that justice will be served and that if anyone is found guilty of wrongdoing that they'll be punished," Trudeau said Tuesday, noting that the government initially resisted Liberal demands to refer the scandal to the RCMP.

Mulcair said he hopes the charges signal the beginning of the end of the Senate, which the NDP wants abolished.

Most senators, Liberal and Conservative alike, declined to comment on the charges now that the matter is before the court.

But Claude Carignan, government leader in the Senate, acknowledged it was "not good news" for the chamber's image to have criminal charges laid against two of its one-time members.

When the Senate voted last fall to suspend Duffy, Wallin and Brazeau without pay, Liberal Sen. George Baker was among those who argued that punishing the trio before they were convicted of any crime could interfere with any subsequent criminal proceedings against them.

Baker said Tuesday he'll be interested to see if the court determines that, having already been sentenced by the quasi-judicial Senate, a trial would constitute double jeopardy for Brazeau.

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