The legal proceedings around Mike Duffy's expenses are finally over, but the Senate could now be on the hook for the senator's legal fees.

A spokesman for the Ontario Ministry of the Attorney General said Crown prosecutors have decided not to appeal Duffy's acquittal one month ago.

Tuesday was the deadline to file an appeal.

Ministry spokesman Brendan Crawley said the Crown has decided there is no legal basis for an appeal.

"The Crown's right of appeal from an acquittal is limited to errors of law, and does not include errors relating to factual matters," Crawley said.

Donald Bayne, Duffy's defence lawyer, said the move is a sign that Justice Charles Vaillancourt's decision last month is "legally unimpeachable."

"This is a determination after close scrutiny by legal experts in the Ministry of the Attorney General that Justice Vaillancourt's decision is legally unimpeachable — no legal error was made which would justify an appeal and there was no misapprehension of the evidence before the court on which the Judge based his factual findings," Bayne said in a written statement.

"The judgment is sound and final legally and factually," Bayne said later in an interview with CBC News outside the Ottawa courthouse. "It's very good news. This ends this legal chapter. It's a fitting end because it's confirmation about the soundness of the judgment."

Bayne said while criminal proceedings against his client have ended, Duffy could now press the Senate to help him recoup some of the money he spent on legal bills.

"I think it's fair to say we'll explore issues unrelated to the criminal trial, such as the Senate policy on indemnification of legal fees and the whole issue of the lack of due process in stripping him of two years' worth of salary and pension benefits — improperly," he said.

Donald Bayne spoke to the CBC's Margo McDiarmid outside the Ottawa Courthouse 1:07

Senators are eligible for legal assistance — or indemnification — if it relates to the carrying out of their

parliamentary function.

Duffy was acquitted in April on 31 criminal charges, including fraud, breach of trust and bribery, stemming from his Senate expenses.

At the time, Duffy's trial judge was critical of the Crown's case, saying that prosecutors failed to prove beyond a reasonable doubt that Duffy acted unlawfully.

The Crown's decision comes a week after the RCMP ended its investigation into Senator Pamela Wallin for questionable travel claims. The Crown also withdrew all criminal charges against retired senator Mac Harb for issues related to his living expenses.

"That leaves poor Senator (Patrick) Brazeau still somewhat twisting in the wind and it seems to me that, quite apart from the issue of reasonable prospect of conviction, the Crown should be asking itself: Is it in the interest of justice to go after this man, at this point?" Bayne said of Brazeau, who is not a client.

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