Canada's Senate has been dealing with a controversy over housing and living expenses that has culminated in audits of the expense claims of four senators.

The issue has raised questions about the Senate's travel and housing allowances for senators who make their primary residency more than 100 kilometres from the capital region, and has put the spotlight on residency requirements.

Here's a look at some key moments in the controversy:

September 2003: Mac Harb (Ontario) appointed to the Senate on the advice of Prime Minister Jean Chrétien.

Dec. 22, 2008: Conservatives Mike Duffy (P.E.I.), Pamela Wallin (Saskatchewan) and Patrick Brazeau (Quebec) among 18 people named to the Senate by Prime Minister Stephen Harper.

June 13, 2012: Auditor General Michael Ferguson recommends the Senate require documentation for more of senators' expense claims, after finding the Senate did not have proper documentation to support living expense claims in two of seven cases examined.

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Marjory LeBreton, government leader in the Senate, has had to address the controversy over the Senate's rules for residency and expenses. (CBC)

Nov. 21, 2012: Marjory LeBreton, government leader in the Senate, asks the Senate's board of internal economy to determine whether Brazeau's housing allowance claims are appropriate, following a CTV report questioning Brazeau's residency and housing expense claims.

Dec. 6, 2012: Senate internal economy committee announces it will conduct an audit to assess "whether all senators' declarations of primary and secondary residence are supported by sufficient documentation." Documentation includes provincial health card, driver's licence and voting registration.

Feb. 4, 2013: P.E.I. Health Minister Doug Currie confirms to CBC News that Duffy applied for a provincial health card just before Dec. 25, 2012.

Feb. 5: CBC News reports that a property tax assessment shows Duffy does not receive a P.E.I. resident tax credit for his Cavendish home.

Feb. 7: Wallin tells reporters on Parliament Hill that her home is in Saskatchewan and she is complying with residency requirements.

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Patrick Brazeau was forced out of the Senate on Feb. 12 pending the outcome of charges of sexual assault and assualt. (Adrian Wyld/Canadian Press)

Feb. 7: Brazeau is arrested on charges of sexual assault and assault. He is immediately removed from the Conservative caucus and appears at a Gatineau, Que., court the next day.

Feb. 8: Senate announces it has hired outside auditor Deloitte to examine the residency declarations and related expenses of Duffy, Brazeau and Liberal Senator Mac Harb. It is also seeking legal advice about Duffy’s residency status.

Feb. 12: The Senate votes to put Brazeau on forced leave pending the outcome of the criminal case.

Feb. 13: In an interview with CBC Radio, Wallin says she has declared for Senate officials that her primary residence is in Saskatchewan. In a separate interview, Wallin says she met with Deloitte for an audit of her travel and living expense claims.

Feb. 13: Harper in question period: "In terms of Senator Wallin, I have looked at the numbers. Her travel costs are comparable to any parliamentarian travelling from that particular area of the country over that period of time. For instance, last year Senator Wallin spent almost half of her time in the province she represents in the Senate. The costs are to travel to and from that province, as any similar parliamentarian would do."

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Senator Pamela Wallin has been questioned by an outside auditor over her travel claims. (Adrian Wyld/Canadian Press)

Feb. 14: Senator David Tkachuk, who heads the Senate's committee of internal economy, says the audit of Wallin's travel expenses began as the first of a series of "random" audits by the committee after the auditor general's June 2012 report critical of the way some senators filed claims.

Feb. 22: Duffy tells CBC News in P.E.I. that he and his wife "are going to voluntarily pay back my living expenses related to the house we have in Ottawa." He blames the expenses controversy on a confusing residency declaration form and unclear rules.

March 1: LeBreton tells CBC News via email that "Senator Duffy maintains a residence in P.E.I. and is qualified to sit in the Senate."

March 26: Auditor Deloitte receives a letter from Duffy's legal counsel stating that Duffy had repaid more than $90,000 in expenses, and would no longer be participating in the audit.

March 27: A revised Public Declaration of Assets (external link) for Harper's chief of staff, Nigel Wright, reveals he no longer holds stock options in the private company RSI Executive Investco LLC.

March 29: Senate figures show Duffy claimed $5,519 in living expenses for the three-month period ending in February, higher than the amount claimed in previous two quarters.

April 18: Duffy appears to tell Global News he is waiting for the results of the outside audit to decide whether to repay any housing and living expenses.

April 19: Duffy issues statement saying he has repaid more than $90,000 in housing and living expenses. Senate committee on internal economy confirms $90,172.24 repayment, but does not say when payment was made.

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Senator Mac Harb resigned from the Liberal caucus last week after he was ordered to repay $51,000 in housing and mileage claims by a Senate committee. (Fred Chartrand/Canadian Press)

April 20: Deloitte receives, from Duffy's lawyer, a copy of a letter Duffy sent to Tkachuk offering to meet with the Senate or Deloitte. Deloitte later says it understood the Senate subcommittee had notified Duffy the "offer to meet with Deloitte would delay the process, and that the subcommittee agreed that there should be no further delays in the process."

May 9: Senate releases outside audits and committee's reports on Brazeau, Duffy and Harb. The committee orders Brazeau and Harb to repay $48,000 and $51,000, respectively. Harb quits the Liberal caucus and vows to overturn the committee's findings; his expenses are to be further audited for the previous seven years. Harb, Brazeau and Duffy are placed under greater scrutiny for a year. Report on Duffy's expenses notes the senator had already repaid $90,000. Senate announces that an audit of Wallin is ongoing.

May 9: Harper in question period: "Mr. Speaker ... an independent external auditor was brought in to examine all of these expenses. He looked obviously at the expenses of three particular senators who have had some difficulty. The auditor has concluded that the rules in place were not clear, however, the Senate itself has decided it expects better judgment from the senators. Senator Duffy some months ago repaid the money and the Senate has decided that other senators will be expected to similarly repay those amounts."

May 12: RCMP confirms it is looking into Senate expense claim audits.

May 14: NDP demands release of legal opinion on Duffy residency. LeBreton says Duffy meets all residency requirements.

May 14: Brazeau says in a press release that he met the Senate's own rules for housing expenses and calls for a public hearing on his case.

May 15: Following a report by CTV News, PMO spokesman Andrew MacDougall confirms the prime minister's chief of staff, Nigel Wright, wrote a personal cheque for $90,172.24 to repay Duffy's living expenses, and says the cheque was a gift, not a loan. Conservative spokesman Fred Delorey says "no party money involved in any way" in Duffy repayment. Duffy and Wright decline comment. Ethics commissioner Mary Dawson says she is reviewing the payment.

May 16: Mike Duffy quits the Conservative caucus to sit as an Independent senator "pending resolution" of the expense questions. "Throughout this entire situation I have sought only to do the right thing. I look forward to all relevant facts being made clear in due course, at which point I am hopeful I will be able to rejoin the Conservative caucus," Duffy says in a statement. PMO says Nigel Wright has the "full confidence" of the prime minister. NDP call on Senate ethics office Lyse Ricard to investigate the Duffy-Wright payment.

May 17: PMO spokesman says Wright is "staying on."

May 17: Pamela Wallin releases a statement saying she has recused herself from the Conservative caucus. Wallin says she has been co-operating "fully and willingly" with auditors and adds that she will have no further comment until the audit process is complete. Senate government leader Marjory LeBreton says in a statement Wallin informed her she has "resigned" from caucus to sit as an Independent.

May 19: Nigel Wright resigns "in light of the controversy surrounding my handling of matters involving Senator Duffy," adding he did not tell Harper of the repayment "either before or after the fact." Harper says in a statement he accepted Wright's resignation "with great regret." Ray Novak, Harper's principal secretary, takes over as chief of staff.

May 21: Prime Minister Stephen Harper allowed journalists into a Conservative caucus meeting while he spoke to his MPs and senators. He told them he was "very upset" about the recent conduct of "some parliamentarians" and his own office but he did not name names and did not specifically address the Senate spending scandal. He did not take questions from reporters and they were asked to leave when he was done speaking. The Senate decided to send Duffy's audit report back to its internal economy committee for a second review.

May 23: Duffy tells reporters Canadians have a right to know the facts and he's prepared to tell "the whole story" at the appropriate time and place. The Senate tables a letter from the RCMP asking for copies of guidelines as part of its review to determine "whether there are grounds to commence a criminal investigation."

May 28: The Senate committee on internal economy voted unanimously to send Duffy's expense claims to the RCMP. The committee normally meets behind closed doors but it was opened up to media and the public. The clerk of the committee described a pattern of Duffy claiming living expenses for Ottawa when he was not in the capital on Senate business.

May 30: CBC reports on emails that reveal Duffy was in consultations with Conservatives about an expanded role in the party and increased compensation including a suggestion he be made a minister.

June 4: Senate ethics office Lyse Ricard suspends her investigation while RCMP are examining the issue.