Two audio experts have independently concluded that the secret recordings made by MP Gurmant Grewal were edited.

John Dooher, a forensic audio engineer hired by CBC News, said Thursday there is a "crude" edit and something "amiss" about a section of tapes made by the B.C. member of Parliament.

The tape has Health Minister Ujjal Dosanjh talking about Grewal's future.

Health Minister Ujjal Dosanjh in Ottawa, Thursday.

Grewal secretly recorded hours of conversations with Dosanjh and Tim Murphy, the prime minister's chief of staff, about switching parties.

"Right here, we hear what sounds like an edit. We have a change in the frequency spectrum so something has changed there," said Dooher, demonstrating the difference while at a sound board.

His conclusions are supported by Stevan Pausak, one of Canada's leading forensic-sound analysts. Pausak was asked by Canadian Press to carry out a similar examination. He said one of the tapes has an abnormal break, indicting a section may have been cut out.

Gurmant Grewal

Dooher said while more sophisticated testing could offer more certainty, he believes his original conclusion.

"This sounds to me, not only that this is an edit, but an edit done with something very crude," he said.

Dosanjh hinted Thursday that Conservative Leader Stephen Harper's office was involved in tampering with the tapes.

"The leader of the Opposition had the tapes for 14 days," Dosanjh said of contentious secret recordings. "What were they doing with them?"

On some of the tapes released this week – two weeks after Grewal first released excerpts – Dosanjh and Grewal can be heard talking in Punjabi about what future Grewal might face with the Liberals.

The health minister told reporters Thursday that "in at least two places, conversations had been spliced in" that had been taken out of context to make him look worse.

Dosanjh said two "independent experts" had confirmed that the tapes had been doctored, but gave no other details.

About 90 minutes of taped conversations were released early this week, though Grewal had said he recorded up to four hours of talks with Dosanjh and Prime Minister Paul Martin's chief of staff, Tim Murphy.

Approached by reporters on Parliament Hill later Thursday, Grewal denied the tapes had been altered before refusing to answer any more questions on the grounds that the RCMP were looking into the matter.

Grewal has said the Liberals came courting him, offering him inducements to switch parties in an effort to keep Martin's minority government alive.

The Conservatives want an inquiry conducted on their allegation that the Liberals tried to buy Grewal's vote, and the Bloc Québécois have asked the RCMP to investigate the matter.

Dosanjh and other top Liberals have said Grewal made the first approach, demanding a cabinet position for himself and an ambassadorship or Senate appointment for his wife, fellow British Columbia Conservative MP Nina Grewal, in return for not voting against the Liberals on a key May 19 confidence motion.

Dosanjh also questioned what had happened to two hours of conversation between himself and Grewal at the health minister's home, which he said would show him repeatedly insisting that no promises of advancement could be made.

"I thought he was coming to talk to me about my own personal experience," said Dosanjh, a former New Democrat premier of British Columbia who switched to the federal Liberal party in April 2004, just before the last general election.

"He wanted to turn that into a bargaining session."