Chuck Cadman, a member of Parliament from British Columbia, died in 2005. (Canadian Press)

A tape recording at the centre of Prime Minister Stephen Harper's $3.5-million defamation suit against the Liberal party was not altered as the prime minister has claimed, a court-ordered analysis of the tape by Harper's own audio expert has found.

The key portion of the recorded interview of Harper by a B.C. journalist contains no splices, edits or alterations, a U.S. forensic audio expert has determined.

The findings may call into question Harper's testimony about the interview during a sworn cross-examination conducted by a Liberal party lawyer in August.

The analysis was filed in Ontario Superior Court on Friday by lawyers for the Liberal party, despite attempts by Harper's lawyer to keep the opinion out of the court file until at least next week.

Harper sued the Liberals in the midst of a raging controversy earlier this year over claims in a book by B.C. author Tom Zytaruk that the Conservatives offered the late Independent MP Chuck Cadman a $1-million life insurance policy in return for help defeating the minority Liberal government in 2005.

The prime minister maintains that Zytaruk doctored the tape of an interview he conducted with Harper after Cadman died.

In an interview with CBC New on Friday, Zytaruk said he felt vindicated by the audio expert's findings.

"I've got these guys accusing me of doctoring the tape. No, you know. I don't like the impact that it has on my family. It's just one ridiculous situation after another over these past months," Zytaruk said.

"I'm finding some redemption in this thing. And I'm happy with our system too, and that this is happening today and that this news is coming out.

"Our government, they can say whatever they want basically about the little guy, and unless you have a barrel of money, you're going to just have to suck it up, you know?"

Harper denies that he told Zytaruk he was unaware of the "details" of the insurance policy offer. He insists that he only confirmed the party had offered Cadman "financial considerations" in return for rejoining the Tories and voting against the Liberals in a Commons confidence vote.

But former FBI agent Bruce Koenig, the sound expert Harper hired to prove his allegations, submitted a report dated Friday to Harper's lawyer, which also had to be sent to the Liberal lawyer Chris Paliare.

In the report, Koenig concluded that the first part of Zytaruk's interview with Harper, which contains the key portions that the prime minister has contested, was intact.

The second part, beginning roughly one minute and 41 seconds into the tape, was a new recording that was made over the final part of the original recording, he said. But the first crucial minute and 41 seconds had not been altered.

Koenig reported that the tape "contains neither physical nor electronic splices, edits or alterations, except for the over-recording start that erased and replaced the end of the first part of the designated interview."

Harper spokesman says finding doesn't undermine case

Kory Teneycke, a spokesman for Harper, maintained that the findings do not undermine the prime minister's case — and in fact can be used to buttress Harper's claims.

"This report supports our position that the tape does not represent the complete interview, and as such is favourable to our case," said Teneycke.

But it's the first portion of the interview — the first one minute and 41 seconds that Koenig says were not tampered with — that is considered key.

That part of the recording includes Zytaruk's question to Harper on whether he knew anything about a $1-million insurance policy that unidentified Conservatives had allegedly offered to Cadman in return for his support in Parliament against the Liberals.

"I don't know the details, I know that, um, there were discussions, um, but this is not for publication?" Harper replies on the tape.

Zytaruk tells Harper his comments are intended for a book Zytaruk was writing about Cadman, who had died earlier that summer in 2005.

Harper again says he "didn't know the details" but adds that he told Conservatives who were going to approach Cadman they were unlikely to succeed.

"They were just, they were convinced there was, there were, financial issues," Harper says. He later qualifies his response to Zytaruk by saying: "Of the, uh, uh, the offer to Chuck was that, it was only to replace financial considerations he might lose due to an election."

Harper told court that tape was edited

When Liberal lawyer Paliare questioned Harper during cross-examination in August, Harper said of Zytaruk's question about the insurance policy: "That is not the question as he put it. He has done some editing there.

"What I do know is that this answer is not the answer to this question, I think there's been some editing in this question, so I don't think it goes from this question to this answer."

Harper insisted in his testimony that at that point in the interview he told Zytaruk he did not know about the offer of an insurance policy. He claimed Zytaruk edited that response out of the recording.

Harper testified that he authorized his campaign manager, Doug Finley, and former adviser Tom Flanagan to approach Cadman only with an offer of financial help should Cadman vote against the Liberals and then run for the Conservatives in the election that would have ensued.

Harper's lawyer, Richard Dearden, convinced Justice Charles Hackland last month to postpone a hearing into the veracity of the audiotape until after the federal election. The two sides have a conference scheduled with Hackland next week on other aspects of the case.