The current head of the RCMP was responsible for giving security clearance to one of Stephen Harper's former top advisers with numerous criminal convictions.

CBC News has learned William 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 Bruce Carson working in the Prime Minister's Office. The RCMP is currently probing allegations that Carson was involved in illegal lobbying.

Elliott, who was hand-picked by Harper to become the Mounties' first civilian commissioner in 2007, 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.

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.

The Prime Minister's Office has asked the RCMP to investigate Bruce Carson, seen here in an interview with CBC News last November. Carson is a former adviser to the prime minister. CBC

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'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.

"I remember going to him and saying to him, 'I've got to fill out these forms," Carson said. "You know I have a criminal past. Should I go ahead and fill them out, or is that sort of the end?' He said, 'No, go ahead and fill them out,' and so I did."

Chief of staff only got 'yea or nay'

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.

"All I got was the yea or nay," he said.

Brodie would not say if Elliott personally briefed him on Carson's security clearance.

The PMO wrote to the RCMP commissioner last month asking the force to investigate Carson after a probe by the Aboriginal Peoples Television Network 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.