ORILLIA - Liberal leader Stephane Dion says Canadians shouldn't believe Stephen Harper's claim that he didn't know the details of a Conservative offer of a life insurance policy to cancer-stricken MP Chuck Cadman in exchange for his support on a key parliamentary vote.

Harper claims a tape recording of an interview in which he says he was aware of the offer was doctored by the journalist. But an expert hired by the Conservatives filed an opinion in court on Friday that contradicts Harper's claim.

"The expert of the Conservative Party confirmed that the tape has not been doctored, that means that Mr. Harper has a lot to explain," Dion told reporters during a campaign stop in Orillia yesterday.

"He (Harper) cannot be silent anymore. He needs to explain why he was trying to tarnish the reputation of a reporter, why he was trying to do that in order to protect his own reputation.

Dion said the incidentraised a question of"how low this man is willing to go to protect his reputation and to hide the facts from Canadian voters before (voting day) next Tuesday."

"We cannot keep this man as prime minister. We cannot believe him any more," Dion said earlier on the same issue during an interview with Global TV. Harper sued the Liberals after they attacked himover his alleged involvement in the Cadman affair. At issue is material from a book by B.C. journalist Tom Zytaruk that says senior Conservatives offered Cadman, an Independent MP who has since died, a $1-million life insurance policy in exchange for his backing in a budget vote in 2005.

Under cross-examination in August, Harper said he believed Zytaruk had altered the tape.

But an analysis by a former FBI sound expert hired by the Conservatives found the early section of the tape that contains the disputed passage had not been altered, according to a lawyer representing the Liberals in the defamation suit filed by Harper against the party.

The analysis did say that there wasanover-recording later in the tape, starting at 1 minute, 41 seconds.

Harper offered only a brief comment on the issue, saying that his version of events is vindicated by another expert's report.

"All these reports show - you know, experts have differences in nuance - but all the latest report shows exactly what we're saying that this tape has been edited and the conversation is incomplete, and you know, that's uh — the Liberal party has a big problem in court, that's all I can say."