Former security adviser Bruce Carson was independently cleared to work in the Prime Minister's Office, and it wasn't until later that the full extent of his criminal record became clear, Stephen Harper said Wednesday.

The Conservative leader was asked at an appearance in Markham, Ont., whether RCMP commissioner William Elliott, who was then working in the Privy Council Office, had been involved in the vetting of Carson, as CBC News has reported.

The prime minister avoided any mention of Elliott's name in his reply. Because the matter has been referred now to the RCMP for review, Elliott would be the person ultimately in charge.

"With respect to the security clearance, this is something that's done independently by the Privy Council Office. It's not done by my office," Harper said, speaking in French.

"I already explained that I was aware of Mr. Carson's difficulties a long time ago .… Now later we learned other things, and I'm not sure why that happened, but that's the reality, and we'll have to look at why that happened, and we will be doing that."

Harper didn't say directly whether he knew the identity of who gave Carson's appointment the green light.

CBC News reported Tuesday that Elliott, who was serving as national security adviser in the Privy Council Office in January 2006, was the official responsible for giving the green light to Carson working in the Prime Minister's Office.

The RCMP is currently probing allegations that Carson was involved in illegal lobbying.

Elliott appointed by Harper

Elliott was hand-picked by Harper to become the Mounties' first civilian commissioner in 2007. He is stepping down in the summer after a controversial reign and public battles with senior RCMP brass over his management style.

The Canadian Press reported earlier this week that Carson was convicted on five counts of fraud — three more than previously known — and received court-ordered psychiatric treatment prior to his hiring as an adviser to Harper.

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Bruce Carson, seen in a 2010 interview, was cleared to work in the Prime Minister's Office by the independent bureaucrats who support the office, Stephen Harper said Wednesday. Harper's former adviser has past fraud convictions.

Carson worked in the Prime Minister's Office until 2008. An investigation into Carson's business dealings by the Aboriginal Peoples Television Network led the PMO to call in the RCMP in March.

More of Carson's past fraud convictions and bankruptcies have surfaced in the news in recent days.

Harper has said he knew Carson had "difficulties with the law" many years ago, but that he didn't know about all of his convictions and that he would not have hired him had he known the full extent of his past legal troubles.

Opposition leaders have slammed Harper over Carson's hiring, questioning how Carson, with his convictions, was able to get into the inner circle of the prime minister.

Carson revealed past: lawyer

Carson's lawyer told CBC News on Monday that Carson was upfront about his fraud convictions during a required security screening.

Patrick McCann, who represented Carson during his past legal troubles and spoke to him Monday, said Carson doesn't have the security clearance application, but he remembers telling them everything.

Carson told The Canadian Press he recalls mentioning his criminal past in early 2006 to Ian Brodie, then Harper's chief-of-staff, when applying for Secret-level clearance.

Brodie told CBC News Tuesday night he had no involvement in granting Carson's security clearance and was only told whether prospective employees "got clearance or not because they can't be hired until they're cleared."

Brodie said he was never actually given the security files on a prospective employee.

The PMO wrote to the RCMP commissioner last month asking the force to investigate Carson after a probe by the APTN alleged the 65-year-old may have illegally lobbied the federal government on behalf of a company that employed his girlfriend, a 22-year-old one-time escort.