By Tim Naumetz, The Canadian Press

OTTAWA - A former FBI scientist hired by Stephen Harper's lawyer in the prime minister's $3.5-million lawsuit against the Liberal party has contradicted two other experts who said an audio tape at the centre of the legal action was doctored, court documents reveal.

The resume of the latest expert Harper's legal team consulted demonstrates the extent to which the prime minister is prepared to go in his claim the Liberals defamed him over allegations of bribery in offers the Tories made to late MP Chuck Cadman as a government confidence vote approached in 2005.

Former FBI special agent Bruce Koenig - who lists expert evidence about former U.S. president Richard Nixon's Watergate tapes and analysis of gun shots in the assassination of John F. Kennedy among his accomplishments - said more evidence is needed to judge the veracity and integrity of the disputed tape recording.

The Conservative party cited the opinions of the first two experts last month when Tory MP James Moore held a news conference to challenge B.C. author Tom Zytaruk's claim that Harper knew Tory operatives offered Cadman a financial incentive to help defeat the Liberal government in May 2005.

The initial two experts, one from the United States and the other from Stratford, Ont., categorically ruled that an audio tape recording of an interview Zytaruk conducted with Harper in September 2005 had been altered.

Harper's lawyer in the defamation suit, Richard Dearden, filed the expert evidence in early June in support of Harper's claim the Liberal party libeled him by suggesting he was aware of attempted bribery in the party talks with Cadman.

One of the initial two experts, the head of Owl Investigations Inc. in Colonia, N.J., said he concluded "with scientific certainty that this tape has been edited and doctored to misrepresent the event as it actually occurred."

That expert, audio authentication engineer Thomas Owen - who lists experience as a consultant to CSI and five U.S. networks on his credentials - claims to have verified the first recorded message from Osama bin Laden after the September 2001 terrorist attacks by al-Qaida was "probably authentic."

The other, Alan Gough, a former TV producer who provided video and audio forensic services to the Toronto police force before becoming a "truth verification" expert, said Zytaruk's interview "is not a continuous recording of one conversation."

Dearden filed both opinions, along with sworn affidavits, in the swelling Superior Court file of Harper's defamation claim, but added Koenig's analysis as he began attempts to get Zytaruk to provide his original version of the interview with Harper. The first two examinations done by Harper's experts were limited to copies of the tape recording Zytaruk had provided Dearden.

Koenig, who also performed an authenticity analysis of the Linda Tripp telephone recordings in the investigation of former U.S. president Bill Clinton, reported irregularities in the copy tape and portions where an earlier recording had been taped over, but concluded Zytaruk's original recording, his tape recorder and an external microphone if Zytaruk used one "are required to conduct a conclusive authenticity examination in a forensic audio laboratory."

That kind of examination is required to "scientifically" determine whether the original information is truly original, contains or has alterations, such as deletions or additions, Koenig said in the report he submitted with his own sworn affidavit.

In the fallout over the original Conservative release of expert evidence, Zytaruk conducted a series of television and other media interviews vigorously denying he had doctored the tape.

On the recording, Harper is heard saying he "understands" two of his top political operatives at the time, Doug Finley and Tom Flanagan, approached Cadman with an offer to replace "financial considerations" he might lose "due to an election."

Zytaruk says Cadman's widow, Dona, told him after Cadman died in 2005 that Cadman told her shortly before the May confidence vote that two Conservatives had offered him a $1-million life insurance policy if he voted against the Liberals to help force an election.

Dona Cadman has not directly denied that claim, although she has signed affidavits Dearden filed in the court case denying some other details of Zytaruk's version of the day he interviewed Harper in front of the Cadman home.

Harper has sworn to two affidavits denying Zytaruk's version of the events. Although the prime minister does not deny using the words "financial considerations," he insists in the court filings he was talking about helping Cadman out with campaign expenses if he were to run as a Conservative.

It later emerged that any discussion of life insurance could have centred on an MP's ability to extend the generous parliamentary plan with cash additions in place of premiums before leaving office.

Dearden has served notice to other lawyers involved in the case that he intends to file a motion in Ontario Superior Court seeking a summons for Zytaruk to personally testify when the first hearings in the case begin in Ottawa in September. Dearden also is planning a motion in a B.C. court seeking Zytaruk's testimony and court authentication of the tape recording in a hearing there.

The Liberal party has filed a statement of defence claiming Harper's lawsuit is an infringement of free political comment and violates the Charter of Rights as well as sections of the Canadian constitution.

The defence statement filed by the party's Toronto lawyer, Chris Paliare, calls the lawsuit an attempt to intimidate the opposition and describes it is a "SLAPP suit - a Strategic Lawsuit Against Public Participants."