The RCMP are seeking personal bank account and credit card records for Senator Mike Duffy as part of their investigation into his expense claims, according to new court documents.

The lead investigator looking into Duffy's claims filed the documents in an Ottawa court Thursday asking that CIBC and RBC banks hand over the information.

Cpl. Greg Horton believes the Prince Edward Island senator committed breach of trust by filing inappropriate travel and housing expense claims. Duffy has not been charged with any crime.

In addition to statements for his personal credit cards and bank accounts, the RCMP want to see Duffy's mortgage application from 2010 and a list of all address changes in relation to any account solely or jointly in Duffy's name related to either his Ottawa home or the one in P.E.I.

Horton filed a similar application to the court in June that asked the Senate to hand over housing declarations, travel expense claims, cellphone bills, Senate credit card statements, and records of expenses paid to and by Duffy.

Those documents are currently being reviewed by Horton's team and the court document obtained Thursday by CBC News also said that the cheque that Nigel Wright, Prime Minister Stephen Harper's former chief of staff, wrote to cover Duffy's expenses is still under investigation.

"Investigators on my team are currently reviewing hundreds of pages of documents provided by Mr. Wright," the document said. Wright resigned as Harper's chief of staff after the secret payment was revealed in the media.

The RCMP started looking at Duffy's expenses in March while an external audit by Deloitte was underway, at the request of the Senate. The firm was also asked to look at the residency expense claims made by senators Patrick Brazeau and Mac Harb and those reports were done in May. An audit on senator Pam Wallin is expected to be released next week.

Duffy said he would pay $90,000 back even before the audit was finished and there were allegations that the Senate went easy on Duffy in its report on the audit as a result. But it was Wright's pocket that the money came out of, not Duffy's, and now that payment is part of the RCMP's investigation.

Harb has paid back $51,000 but under protest and is fighting the Senate in court. Brazeau is refusing to pay any money back and his salary is being garnisheed.

Senators can be reimbursed by the government for travel between their home province and Ottawa and up to $22,000 per year can be claimed for housing in Ottawa, if they declare their primary residence is more than 100 kilometres outside the capital.

Pattern of 'fraudulent' claims

Duffy, a former journalist, has had a home in Ottawa since 1971 and has a cottage in Prince Edward Island, the province he was appointed to represent by Harper in December 2008. He claims the home in P.E.I. as his primary residence and collects the housing allowance.

The court documents indicate some of the reasons why the RCMP doesn't believe Duffy's primary residence is in P.E.I. His driver's licence history, for example, consistently lists Ottawa as his home. He only got a P.E.I. licence in 2009.

In December, around the same time that all senators were asked to provide copies of their health card and driver's licences to the Senate to prove their residency Duffy called the office of P.E.I's health minister and asked for a health card application to be expedited, and asked that the request be confidential, according to the RCMP.

The court document filed Thursday also notes that Duffy's banking address was changed from an Ontario address to a Cavendish address on Dec. 10, 2012, just days after the Senate said it was looking into senators' residency declarations.

The RCMP are also digging into per diem claims that Duffy made and believes some were "fraudulent" and amount to breach of trust. Some per diems were claimed on days when Duffy was in Florida (Duffy has said those were claimed in error), others while he was in P.E.I., not in Ottawa on Senate business, and others were claimed while he was campaigning in the 2011 election.

Horton notes that Mark Grenon, a chartered accountant who is a certified fraud examiner, has been seconded from public works to the RCMP. It was through his examination of Duffy's expenses that he came across the personal credit cards that Duffy used to pay Senate expenses.

He has a Senate-issued credit card but used his personal ones to rent cars and hotel rooms and buy train and airline tickets. He would then submit expense claims to be reimbursed.

Some of Duffy's expense claims were handwritten, "often with several amendments and corrections," the court document said.

"I believe that Senator Duffy has demonstrated a pattern of filing fraudulent expense claims," Horton wrote. "He maintains that his primary residence is in P.E.I. so that he can collect housing and travel allowances from the Senate, however uses his Ottawa residence as his primary residence when convenient, such as when dealing with OHIP so that he can obtain medical coverage in Ontario."