Auditor General Michael Ferguson has issued final audit letters to 117 current and former senators, including five to 10 whose expense claims are being flagged for egregious patterns of behaviour, CBC News has learned.

Sources tell CBC News that Ferguson, who has been conducting a review of all senators' expenses over the past two years, has found "a few people with big issues."

Ferguson will release his final results in the first week of June — and the RCMP are watching the results closely, CBC has learned. No decision has been made about whether senators who have the most serious expense issues will be identified in the auditor general's report.

Conservative senators and those who were appointed as Liberals have been bracing for the results of the audit ever since investigations were launched by the RCMP into the spending habits of suspended Senator Mike Duffy and three of his Senate colleagues: suspended senators Patrick Brazeau and Pamela Wallin and retired senator Mac Harb.

Duffy is currently on trial facing 31 charges of fraud, breach of trust and bribery. Duffy has pleaded not guilty and his lawyer has attempted to portray his spending habits as typical of what occurred among those appointed to the Red Chamber.

Letters sent to senators

Ferguson sent out letters to all the senators whose spending has been divided into three general categories: the five to 10 senators exhibiting a pattern of troublesome expensing; those with some administrative problems; and approximately 40 senators who were cleared.

A one-page letter sent to those who were cleared informs them that their expenses will not be part of the auditor general's report. The letter was signed by Ferguson.

Ferguson wouldn't comment on the content of the letters and declined to offer specifics about the upcoming report, saying only that it will be presented in June and have the results of the Senate expenses audit.

"Then it goes to the Senate, for them to make the decision about what to do with what we found," he told CBC News.

The process took around two years rather than the 18 months expected to complete the process.

"It's certainly taken us more time than we originally thought," Ferguson said.

Staff from Ferguson's office were walking the halls of the Senate handing out the final audit reports the week of April 20. Senators will have the opportunity to send a 500-word response that will be incorporated into the auditor general's final report.

Those whose expenses are red-flagged as troubling could ultimately see their reports referred to the RCMP by the Senate standing committee on internal economy — but that may not be necessary in this case. The RCMP can investigate those cases without a referral, as they did in the Duffy case.

In the case of Duffy, the RCMP didn't wait for an official invitation from the Senate to start their investigation. In court documents, ﻿Sgt. Greg Horton, the RCMP's lead investigator, said the Duffy case commenced in March 2013 after several media stories were published. The Senate only referred Duffy's case to authorities two months later, in May.