The RCMP are looking for a chain of emails and documents that support Mike Duffy's allegations that the Senate expenses scandal reaches right into the Prime Minister's Office, CBC News has learned.

"The existence of such documentation may potentially be evidence of criminal wrongdoing by others," says Supt. Biage Carrese from the RCMP National Division in a Nov. 1 letter obtained by CBC News and subsequently released publicly by Duffy Tuesday.

The Mounties are particularly interested in Duffy's claim that his initial story about repaying his disputed expenses by taking out an RBC loan was concocted by senior advisers to Prime Minister Stephen Harper.

"Emails from the PMO specifically relating to a script for Senator Duffy to follow in advance of obtaining funds from a RBC loan to repay the Receiver General" may be material to the RCMP's investigation, Carrese wrote.

Duffy initially told Canadians that he and his wife had taken out a loan from RBC and repaid the $90,000 in ineligible expenses in March.

But last week, Duffy told the Senate, "On Feb. 21, after all of the threats and intimidation, I reluctantly agreed to go along with this dirty scheme."

Duffy alleged for the first time last week "that line" about the RBC loan was part of a plan fabricated by the PMO "to deceive Canadians as to the real source of the $90,000."

"That line about RBC was part of a script written for me and emailed to me by the PMO," Duffy said.

The former Conservative senator said the PMO seized on the fact that he and his wife were taking out a line of credit to renovate their home as cover for Nigel Wright's decision to give Duffy $90,000 out of his own pocket to repay the senator's inappropriate expenses. Wright was Harper's chief of staff until a media report revealed the deal.

"Senator Duffy intimated that he is in possession of emails and documents which may be material to our criminal investigations," said the officer in charge of sensitive and international investigations for the RCMP in the letter.

A spokesman for Harper said the office is working with the RCMP.

"We have received no such letter from the RCMP. As we have already stated, we are actively assisting the RCMP in their investigation," Jason MacDonald said in an email.

Circle around PM grows

The other emails the RCMP are seeking relate to a Dec. 4, 2012, email from Wright to Duffy acknowledging the senator's expenses were in order, and an email dated Jan. 6, 2009, from Christopher McCreery, who worked in Senator Marjory LeBreton's office, about residency policy.

"My investigators are interested in gathering all evidence respecting this matter in order to conduct a thorough investigation," said Carrese in his letter obtained by CBC News.

Duffy tabled the Wright and McCreery emails in the Senate last week, but not the chain of emails from the PMO which he said included a script about the RBC loan to repay his ineligible expenses.

Reached about the letter on Monday, the RCMP told CBC News they had no comment.

The alleged coverup, according to Duffy, involved the Prime Minister's Office, former PMO lawyer Benjamin Perrin, the Conservative Party lawyer Arthur Hamilton, and Duffy's lawyer Donald Bayne.

"When you look at all those emails in that chain, it proves this was a setup from the start and that I am innocent," Duffy said in his speech to the Senate.

An email exchange between Duffy and former PMO issues manager Chris Woodcock also surfaced publicly last week, after Duffy spoke to the Senate on Monday.

In an email dated May 15, the morning after CTV News first reported that Wright and Duffy had come to a secret deal to help the senator repay his ineligible expenses, Woodcock asked Duffy: "Can you confirm whether you advised the Senate ethics officer of any loans/gifts involved in the March 25th repayment?"

"Trying to cover off all the angles," Woodcock wrote.

It is not clear from the email exchange whether Woodcock knew of the alleged scheme that would see Duffy say he used his own funds to repay ineligible expenses that had in fact been paid by Wright.

News of the RCMP seeking emails and documents from the PMO comes on the heels of another Conservative revealing what he knew about Wright's decision to repay Duffy's ineligible expenses.

In an update to party members gathered at the Conservative Party's annual convention in Calgary on Saturday, Senator Irving Gerstein conceded that he and Wright did discuss paying back Duffy's inappropriate expenses.

Gerstein said he told Wright the party would not pay for Duffy's disputed expenses and "it never did."

The Conservative Party fund was, however, used to repay Duffy's legal fees, Gerstein confirmed. Last Monday, Duffy alleged that Wright had arranged not one cheque, but two.

Harper has maintained all along he knew nothing about the $90,000 his right-hand man gave to Duffy, saying the one person responsible for this "deception" is Wright.

During the course of their investigation, the RCMP have said that Wright provided investigators with hundreds of pages of emails, as well as a binder labelled with Duffy's name.