The opposition says Prime Minister Stephen Harper must wear the blame for a Senate expenses scandal that happened under his watch and which has resulted in 31 criminal charges being laid against Senator Mike Duffy by the RCMP today.

The RCMP announced Thursday Duffy faces charges of bribery of a judicial office holder, frauds on the government and 29 other charges related to Senate expenses, the awarding of consultant contracts and the acceptance of the $90,000 payment from Wright.

"This entire issue is the result of the prime minister's poor judgment," MP Marc Garneau told reporters gathered in Ottawa on Thursday.

"Poor judgment in appointing Mike Duffy to the Senate when he clearly didn't meet residency requirements, poor judgment in fostering a culture in the PMO where his inner circle thought it was OK to write a $90,000 cheque to a sitting Senator then covering it up with a whitewashed Senate report."

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Liberal MP Marc Garneau says Prime Minister Stephen Harper's 'poor judgment' is to blame for the criminal charges that have been laid against Senator Mike Duffy. (Justin Tang/The Canadian Press)

No charges have been laid against Harper's former chief of staff Nigel Wright, who gave Duffy the money to repay his ineligible senate expenses. Wright resigned last year after news of his payment became public.

"Throughout this entire PMO ethics scandal, the prime minister has tried to evade responsibility. His story, what he knew and when, was replete with contradictions. Canadians deserve the truth," Garneau said.

Harper should be compelled to testify: MPs

The NDP's Nycole Turmel echoed Garneau's statement, blaming Harper's poor judgment for appointing Duffy in the first place.

"Let's not forget, these charges in the scandal stem from the poor judgment of a prime minister who appointed Mike Duffy to the Senate, hired Nigel Wright as his chief of staff, and allowed a culture of corruption to fester in Ottawa."

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NDP MP Nycole Turmel says Prime Minister Stephen Harper should be compelled to testify in the Duffy case. (Justin Tang/The Canadian Press)

"The buck stops with Stephen Harper," Turmel said.

The RCMP said Duffy is scheduled to appear in an Ottawa court on Sept. 16.

Both Garneau and Turmel said Harper should be compelled to testify under oath in Duffy's case, saying this would be the only way to get clear answers from him.

Asked about the criticism levelled against the prime minister, Harper's chief spokesman told CBC News "through the charges laid today, the RCMP has made it clear who they believe is guilty of wrongdoing.

"They have also made clear that they do not believe the prime minister had any knowledge of the scheme involving repayment of Mr. Duffy’s inappropriate expenses," Jason MacDonald said.

$90,000 bribery?

Included in the 31 criminal charges laid against Duffy are one count each of bribery, frauds on the government and breach of trust related to the $90,000 payment Duffy received from Wright.

Garneau said it is not clear why Duffy was charged with a count of bribery when he took the money from Harper's former chief of staff chief, but that Wright wasn't charged for giving the senator the cash to repay his ineligible expenses.

"When you are alleging that, there has to be bribery against or to somebody and therefore it implies knowledge beyond Mr. Duffy himself.

"Why, if that is the case, have we not heard about this?" Garneau asked.

The RCMP said in April that "the evidence gathered does not support criminal charges against Mr. Wright."

Wright's lawyer, Peter Mantas, told the CBC's Rosemary Barton Thursday evening that no deal was cut with the RCMP or the Crown to avoid prosecution. Wright has been told to be prepared to testify.

Wright declined comment Thursday.