OTTAWA - One of Canada's top audio experts says someone hired him to analyze the explosive recording at the heart of the Chuck Cadman affair.

But Stevan Pausak won't say who.

He also refused to discuss when he did the work, saying only that it was "a long time ago.''

Pausak, an experienced forensic scientist who holds a doctorate from the Massachusetts Institute of Technology, declined all further comment other than to say he completed an analysis.

"I don't release the name of clients -- regardless if I have the confidentiality agreement or not, it's always confidential,'' he said in an interview from Oakville, Ont.

The revelation adds a mysterious plot twist to the already murky and convoluted story of the Cadman affair and its controversial tape.

On the recording, then-Opposition leader Stephen Harper tells Cadman biographer Tom Zytaruk that some sort of offer was made to the dying Independent MP "to replace financial considerations he might lose due to an election.''

The Tories have not questioned the accuracy of that key quote.

However, the Prime Minister's Office -- citing the analysis of two audio experts that the Conservative party hired, neither of them Pausak -- alleges the tape was tampered with to make it seem like Harper was talking about an insurance policy when he was actually talking about election expenses.

The three opposition parties deny asking anyone to analyze the tape.

"The publisher and author are on the record saying the tape is unedited. That's good enough for us,'' Liberal spokesman Mark Dunn said in an e-mail.

The Conservatives did not respond to questions arising from Pausak's claim.

Harper's communications director, Sandra Buckler, and Conservative spokesman Ryan Sparrow would not say whether other forensic audio experts were consulted by the party, beyond the two who were publicly identified.

They also did not respond when asked directly whether Pausak analyzed the tape for the party, or whether the party demanded confidentiality agreements.

Conservative MP James Moore, the government's designated point-man on the Cadman affair, likewise didn't return a call asking for comment.

 Tape at centre of a $2.5-million lawsuit

Zytaruk says he was the only one recording his interview with Harper on the doorsteps of Dona Cadman's Surrey, B.C., home on Sept. 9, 2005.

He and Howard White of Harbour Publishing insist no one had access to the recording until the publisher began selling tapes to media outlets on Feb. 28.

Zytaruk says he gave copies of his original cassette tape to the RCMP, Harper's lawyers and the Liberals' lawyers after a copy of his manuscript was leaked in late February.

Harbour's lawyers listened to the tape before the book was published but didn't have it scrutinized by audio experts, White said.

Former prime minister Paul Martin wrote the book's foreword and received a copy of the manuscript, Zytaruk said. He added Martin did not receive a copy of the tape. A source close to Martin backed that claim.

Harper filed a court motion this month to stop the Liberals from using the allegedly "doctored'' audio tape to discredit him in the Cadman affair.

Two audio specialists hired by the Tories signed sworn affidavits claiming the tape had either been edited, or was not a continuous recording of one conversation.

Audio specialists Alan Gough of Stratford, Ont., and Tom Owen of Colonia, N.J., declined comment. They also refused to say whether anyone else scrutinized the recording.

When the tape first surfaced, the Liberals accused Harper of trying to bribe a member of Parliament. But an RCMP investigation found no evidence of a crime.

Harper has filed a $2.5-million lawsuit against the Liberals over allegations he knew about a bribery attempt.

Cadman's widow maintains that a pair of Tory operatives offered her cancer-stricken husband a million-dollar life-insurance policy in exchange for his support in a critical showdown in the House of Commons.

The alleged offer was made on the eve of a historic May 2005 vote in which Martin's minority Liberal government hung in the balance. But Cadman voted with the government. He died months later.

Court filings say Harper's close confidants Doug Finley and Tom Flanagan met Cadman for 15 minutes on May 19, 2005, the day of the vote.

Dona Cadman -- the Conservative candidate in her late husband's B.C. riding -- has said she considers the alleged offer a bribe. She reiterated the life insurance claim in court documents filed last month.

Three years ago, Pausak analyzed secret recordings for The Canadian Press made by former Tory MP Gurmant Grewal.