Prime Minister Stephen Harper blamed the bureaucracy for providing security clearance to one of his advisers who was convicted of fraud in the 1980s and 1990s, saying he would not have hired Bruce Carson had he been aware of the extent of his crimes.
However, Mr. Carson insisted that he was forthright about all of his convictions on fraud-related matters in his dealing with the government, including two charges in the 1980s and three in the 1990s.
His case has the Conservatives scrambling to protect their record in government from renewed opposition attacks on the campaign trail.
"Can you trust a Prime Minister who employs a man like Bruce Carson?" Liberal Leader Michael Ignatieff said at a rally in St. John's on Monday. "This is a Prime Minister who talks tough on crime everywhere but in his own office."
Conservative officials said they knew of Mr. Carson's initial brush with the law, but not the second one, which has undermined his claim to be rehabilitated.
When Mr. Harper became Prime Minister in 2006, Mr. Carson obtained a secret-level security clearance from the government and worked in the Prime Minister's Office in many capacities, including advising on energy and environmental issues.
Mr. Carson is now facing an RCMP investigation on allegations of unregistered lobbying for a water-filtration company after he left the PMO in 2008.
Mr. Harper came to power on a promise to restrict lobbying activities and clean up Ottawa. Campaigning on Monday, Mr. Harper told reporters he knew only some of Mr. Carson's background.
"I knew that Mr. Carson had difficulties with the law many, many years ago - some 25 years ago... After that, he had a good employment record. He had worked on Parliament Hill for many decades... He was well regarded."
He said he doesn't know why he was kept in the dark on the full extent of Mr. Carson's criminal record.
"Had I known these things, obviously I wouldn't have hired him," the Conservative leader said after a campaign stop in Ontario's Niagara region. "I don't know why I did not know. Obviously, … Privy Council Office is going to have to look at its systems to make sure these things get caught."
Mr. Carson told the Canadian Press that he mentioned his criminal history in early 2006 to Ian Brodie, then Mr. Harper's chief of staff, and hid nothing when filling out the form.
"Certainly, my belief is that I listed all of the criminal offences to which I had been convicted. I had a discussion with Ian Brodie about this," Mr. Carson said.
The Privy Council Office, which is the top bureaucratic arm of the government, refused to say what it knew about Mr. Carson's criminal past when it approved his hiring.
Mr. Brodie said that he learned of the second set of charges in the media.